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               XTide:  Harmonic tide clock and tide predictor

                             San Francisco graph

Preface

   Welcome to the verbose documentation for XTide 2.  If you are reading
   this as a text file, please be aware that the text was extracted from
   the illustrated HTML version of the documentation that resides at
   [1]http://www.flaterco.com/xtide/.  The web version may also be more
   up-to-date than what you are reading.
     __________________________________________________________________

    THE XTIDE SOFTWARE DISTRIBUTION IS AVAILABLE FROM:
    [2]http://www.flaterco.com/xtide/files.html
     __________________________________________________________________

   [3]Buoy in the mist

Contents

     * [4]License and disclaimer ("NOT FOR NAVIGATION," "ABSOLUTELY NO
       WARRANTY")
     * Verbose documentation
          + [5]Introduction
          + [6]System requirements
          + [7]Installation instructions for supported platforms
          + [8]Available ports for unsupported platforms
          + [9]Modes and formats
          + [10]Using the interactive interface
          + [11]Advanced usage
          + [12]Using the command line interface
          + [13]Running the web server
          + [14]Customizing XTide
          + [15]What to do if your location isn't listed
          + [16]Quirks, limitations, and bugs
          + [17]FAQ
          + [18]Design notes
          + [19]Credits
          + [20]Bibliography
          + [21]Appendix A -- Historical predictions and Y2038 compliance
          + [22]Appendix B -- Application of offsets for Min Flood and Min
            Ebb events
          + [23]Appendix C -- Making calendars fit onto a single page
     * Short attention span documentation for experienced XTide users
          + [24]Differences from XTide 1
          + [25]Quick install instructions
          + [26]Change log
          + [27]News (current XTide developments)

   The XTide software distribution resides at
   [28]http://www.flaterco.com/xtide/files.html.

   Hint:  If you have no idea what all this is about, try reading the
   [29]FAQ first.

   -- David Flater (dave@flaterco.com)

References

   1. http://www.flaterco.com/xtide/
   2. http://www.flaterco.com/xtide/files.html
   3. http://www.flaterco.com/
   4. http://www.flaterco.com/xtide/disclaimer.html
   5. http://www.flaterco.com/xtide/introduction.html
   6. http://www.flaterco.com/xtide/sysreq.html
   7. http://www.flaterco.com/xtide/installation.html
   8. http://www.flaterco.com/xtide/ports.html
   9. http://www.flaterco.com/xtide/modes.html
  10. http://www.flaterco.com/xtide/interactive.html
  11. http://www.flaterco.com/xtide/advanced.html
  12. http://www.flaterco.com/xtide/tty.html
  13. http://www.flaterco.com/xtide/xttpd.html
  14. http://www.flaterco.com/xtide/settings.html
  15. http://www.flaterco.com/xtide/harmonics.html
  16. http://www.flaterco.com/xtide/bugs.html
  17. http://www.flaterco.com/xtide/faq.html
  18. http://www.flaterco.com/xtide/design.html
  19. http://www.flaterco.com/xtide/credits.html
  20. http://www.flaterco.com/xtide/bibliography.html
  21. http://www.flaterco.com/xtide/time_t.html
  22. http://www.flaterco.com/xtide/mincurrents.html
  23. http://www.flaterco.com/xtide/pound_to_fit.html
  24. http://www.flaterco.com/xtide/xtide1diff.html
  25. http://www.flaterco.com/xtide/quickinst.html
  26. http://www.flaterco.com/xtide/changelog.html
  27. http://www.flaterco.com/xtide/news.html
  28. http://www.flaterco.com/xtide/files.html
  29. http://www.flaterco.com/xtide/faq.html

################################################################

   [1]-> Next [2]Contents

Icon License and disclaimer

   NOTE.  The license and disclaimer appearing below applies to the XTide
   program itself.  For information about permissions on the harmonic
   constants, see
   [3]http://www.flaterco.com/xtide/harmonics_boilerplate.txt and
   [4]http://harmonics.unh.edu/xtide/harmonics_boilerplate.txt.

                     XTide Copyright  1998 David Flater

   This software is provided under the terms of the GNU General Public
   License, either version 3 of the License, or (at your option) any later
   version.

   Although the package as a whole is GPL, some individual source files
   are public domain.  Consult their header comments for details.

                             NOT FOR NAVIGATION

   This program is distributed in the hope that it will be useful, but
   WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  The author
   assumes no liability for damages arising from use of this program OR of
   any 'harmonics data' that might be distributed with it.  For details,
   see the appended GNU General Public License.

   (Accurate tide predictions can only be made if the 'harmonics data' for
   the relevant location are good.  Unfortunately, the only way the
   maintainer of those data has of knowing when they are bad is when
   someone with access to authoritative tide predictions or observations
   reports a problem.  You should not use this program or any data files
   that might be distributed with it if anyone or anything could come to
   harm as a result of an incorrect tide prediction.  NOAA and similar
   agencies in other countries can provide you with certified tide
   predictions if that is what you need.)

   XTide's predictions do not incorporate the effects of tropical storms,
   El Nio, seismic events, subsidence, uplift, or changes in global sea
   level.
     __________________________________________________________________

   The tide prediction algorithm used in this program was developed with
   United States Government funding, so no proprietary rights can be
   attached to it.  For more information, refer to the following
   publications:

     Manual of Harmonic Analysis and Prediction of Tides.  Special
     Publication No. 98, Revised (1940) Edition (reprinted 1958 with
     corrections; reprinted again 1994).  United States Government
     Printing Office, 1994.

     Computer Applications to Tides in the National Ocean Survey.
     Supplement to Manual of Harmonic Analysis and Prediction of Tides
     (Special Publication No. 98).  National Ocean Service, National
     Oceanic and Atmospheric Administration, U.S. Department of Commerce,
     January 1982.
     __________________________________________________________________

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   Version 3, 29 June 2007

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   Nothing in this License shall be construed as excluding or limiting any
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    12. No Surrender of Others' Freedom.

   If conditions are imposed on you (whether by court order, agreement or
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    13. Use with the GNU Affero General Public License.

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   END OF TERMS AND CONDITIONS

  How to Apply These Terms to Your New Programs

   If you develop a new program, and you want it to be of the greatest
   possible use to the public, the best way to achieve this is to make it
   free software which everyone can redistribute and change under these
   terms.

   To do so, attach the following notices to the program.  It is safest to
   attach them to the start of each source file to most effectively state
   the exclusion of warranty; and each file should have at least the
   "copyright" line and a pointer to where the full notice is found.
    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

   Also add information on how to contact you by electronic and paper
   mail.

   If the program does terminal interaction, make it output a short notice
   like this when it starts in an interactive mode:
    <program>  Copyright (C) <year>  <name of author>
    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

   The hypothetical commands `show w' and `show c' should show the
   appropriate parts of the General Public License.  Of course, your
   program's commands might be different; for a GUI interface, you would
   use an "about box".

   You should also get your employer (if you work as a programmer) or
   school, if any, to sign a "copyright disclaimer" for the program, if
   necessary.  For more information on this, and how to apply and follow
   the GNU GPL, see <[6]http://www.gnu.org/licenses/>.

   The GNU General Public License does not permit incorporating your
   program into proprietary programs.  If your program is a subroutine
   library, you may consider it more useful to permit linking proprietary
   applications with the library.  If this is what you want to do, use the
   GNU Lesser General Public License instead of this License.  But first,
   please read <[7]http://www.gnu.org/philosophy/why-not-lgpl.html>.
     __________________________________________________________________

   [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/introduction.html
   2. http://www.flaterco.com/xtide/xtide.html#contents
   3. http://www.flaterco.com/xtide/harmonics_boilerplate.txt
   4. http://harmonics.unh.edu/xtide/harmonics_boilerplate.txt
   5. http://fsf.org/
   6. http://www.gnu.org/licenses/
   7. http://www.gnu.org/philosophy/why-not-lgpl.html
   8. http://www.flaterco.com/xtide/introduction.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Bald Head Cliff, Ogunquit, Maine, 1998-06-15

Introduction

   XTide is a package that provides tide and current predictions in a wide
   variety of formats.  Graphs, text listings, and calendars can be
   generated, or a tide clock can be provided on your desktop.

   XTide can work with X-windows, plain text terminals, or the web.  This
   is accomplished with three separate programs:  the interactive
   interface (xtide), the non-interactive or command line interface
   (tide), and the web interface (xttpd).

   The algorithm that XTide uses to predict tides is the one used by the
   [5]National Ocean Service in the U.S.  It is significantly more
   accurate than the simple tide clocks that can be bought in novelty
   stores.  However, it takes more to predict tides accurately than just a
   spiffy algorithm--you also need some special data for each and every
   location for which you want to predict tides.  XTide reads these data
   from harmonics files.  See [6]http://www.flaterco.com/xtide/files.html
   for details on where to get one.

   Ultimately, XTide's predictions can only be as good as the available
   harmonics data.  Due to issues of data availability and of
   compatibility with non-U.S. tide systems, the predictions for U.S.
   locations tend to be a lot better on average than those for locations
   outside of the U.S.  It is up to you to verify that the predictions for
   your locale match up acceptably well with the officially sanctioned
   ones.
     * Deviations of 1 minute from official predictions are typical for
       U.S. locations having the latest data.
     * Deviations of 20 minutes are typical for non-U.S. locations or U.S.
       locations that are using obsolete data.
     * Much longer deviations indicate a problem.

   The XTide software distribution resides at
   [7]http://www.flaterco.com/xtide/files.html.

   XTide and its documentation are maintained by David Flater
   (dave@flaterco.com).
     __________________________________________________________________

   [8]<- Previous [9]-> Next [10]Contents

References

   1. http://www.flaterco.com/xtide/disclaimer.html
   2. http://www.flaterco.com/xtide/sysreq.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://oceanservice.noaa.gov/
   6. http://www.flaterco.com/xtide/files.html
   7. http://www.flaterco.com/xtide/files.html
   8. http://www.flaterco.com/xtide/disclaimer.html
   9. http://www.flaterco.com/xtide/sysreq.html
  10. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Cutler in the fog

System requirements

  Hardware

   The base configuration for which XTide 2 was written was a 166 MHz
   Pentium PC with 32 MiB of RAM (circa 1997).  XTide version 2.9 was
   successfully tested on the same PC in 2007, although by that time the
   RAM had been expanded to 96 MiB.  Comparable non-PC hardware (e.g., Sun
   Sparcstation) also works.

   XTide uses less than 10 MB of memory for a typical interactive session.

  Operating system

   XTide is Unix software.  It is intended to compile and run correctly on
   any reasonably modern version of Unix.  However, I no longer have
   direct access to any flavor of Unix other than Linux, so I can only
   make portability fixes if and when issues are reported.

   In order for tide predictions to have the correct Daylight Savings Time
   (Summer Time) adjustments, your platform must provide a sufficiently
   up-to-date version of the tz database.  This has recently become an
   issue again since the U.S. changed its Daylight Savings Time rules for
   2007.  If your time zone database is obsolete, you may be able to
   upgrade it using the latest version from
   [5]ftp://elsie.nci.nih.gov/pub/ or by installing an operating system
   patch.

   Some non-Unix platforms have limited support:

     * XTide can be run under Windows using [6]Cygwin.
     * A native Windows binary for the command-line client can be built
       using [7]Visual C++ Express Edition.
     * XTide has been ported to a variety of other operating systems with
       differing levels of success as detailed in the [8]ports section.

  Software

   XTide is intended to compile under any reasonably modern C++ compiler
   that supports the Standard Template Library.  However, I no longer have
   direct access to any compiler other than GCC, so I can only make
   portability fixes if and when issues are reported.

   For GCC, "reasonably modern" means version 3.4 or newer.

   You need [9]bzip2, [10]7-Zip or some other archiver that supports the
   bzip2 format to uncompress the files.  A list of libraries on which
   XTide is dependent is provided in the [11]next section.
     __________________________________________________________________

   [12]<- Previous [13]-> Next [14]Contents

References

   1. http://www.flaterco.com/xtide/introduction.html
   2. http://www.flaterco.com/xtide/installation.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. ftp://elsie.nci.nih.gov/pub/
   6. http://www.flaterco.com/xtide/installation.html#cygwin
   7. http://www.flaterco.com/xtide/installation.html#VC++
   8. http://www.flaterco.com/xtide/ports.html
   9. http://www.bzip.org/
  10. http://www.7-zip.org/
  11. http://www.flaterco.com/xtide/installation.html
  12. http://www.flaterco.com/xtide/introduction.html
  13. http://www.flaterco.com/xtide/installation.html
  14. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Prospect Harbor Pt. Light, Prospect Harbor, Maine, 1998-06-14

Installation instructions for supported platforms

  Assumptions

   These installation instructions assume that you are building from
   sources obtained from [5]http://www.flaterco.com/xtide/files.html.
   However, some Linux users may be able to shortcut this process:  XTide
   has been included in [6]Fedora and [7]Debian.  (Thanks to the relevant
   package maintainers.)

   These instructions also assume that you are building XTide version
   2.9.  Previous versions of XTide were not packaged with [8]GNU
   automake, so the installation process was not as standardized.  In
   addition, they statically linked with an included version of libtcd
   instead of using a shared libtcd that was installed separately.  For
   these reasons and others it is advisable that you upgrade to XTide 2.9.

  Dependencies

   In addition to the minimal set of X11 libraries that pretty much
   everyone has, you need the following libraries:

     * [9]libXpm 3.4 or newer compatible version
     * [10]libpng version 0.96 or newer compatible version
     * [11]zlib (a.k.a. libz) version 1.0.4 or newer compatible version
     * [12]libtcd version 2.2 or newer compatible version

   XTide 2.9 will link with [13]libdstr (version 20070215 or compatible)
   if it is found on the system, but installing it is completely
   optional.  If it is not present, XTide will link statically with a
   bundled copy of Dstr.

   tide and xttpd can be compiled in the absence of X11 libraries and
   libXpm.  However, you still need the other stuff.

  Downloading

   Mandatory:  You need the XTide source code distribution, available in
   bzipped tar format at
   [14]http://www.flaterco.com/xtide/files.html#xtide.

   Mandatory:  You need at least one harmonics file.  Harmonics files
   contain the data that are required for XTide to predict tides for
   different locations.  Canonical harmonics files and information on
   getting others is provided at
   [15]http://www.flaterco.com/xtide/files.html#harmonicsfiles.

   Optional:  If you want to enable XTide to draw coastlines on the map,
   you will also have to download the World Vector Shoreline (WVS) files,
   which are available in bzipped tar format at
   [16]http://www.flaterco.com/xtide/files.html#WVS.

   WVS is optional because the minimum recommended hardware (166 MHz
   Pentium PC) takes 16 seconds to draw shorelines for a hemisphere of the
   globe.  A 3.2 GHz P4 takes less than 1 second.

  Installing a harmonics file

   First you need to decompress it.  You can use the command-line tool
   [17]bzip2 as shown below, or you can use [18]7-Zip or any other
   archiver that supports the bzip2 format.

bzip2 -d harmonics-dwf-YYYYMMDD-free.tcd.bz2

   Then move the uncompressed TCD file to a permanent location, e.g.,
   /usr/local/share/xtide, and make it world readable:

mkdir /usr/local/share/xtide
chmod 755 /usr/local/share/xtide
chmod 644 harmonics-dwf-YYYYMMDD-free.tcd
mv harmonics-dwf-YYYYMMDD-free.tcd /usr/local/share/xtide

  Installing the World Vector Shoreline files (optional)

    1. Create a directory to contain the WVS files.
    2. Change your current working directory to that directory.
    3. Unpack the tar file in that directory.

   Under Linux and any other system with GNU tar:

tar xvjf wvs.tar.bz2

   Elsewhere:

bzip2 -dc wvs.tar.bz2 | tar xvf -

  Unpacking the sources

   Under Linux and any other system with GNU tar:

tar xvjf xtide-2.xyz.tar.bz2

   Elsewhere:

bzip2 -dc xtide-2.xyz.tar.bz2 | tar xvf -

  Configuring

    I.  Specify the location of the harmonics file(s)

   There are two ways to do this.

    1. The first way is by setting the environment variable HFILE_PATH.

export HFILE_PATH=/usr/local/share/xtide/harmonics.tcd

       In the event that you have more than one harmonics file that you
       wish to use simultaneously, list them separated by colons.

export HFILE_PATH=/usr/local/share/xtide/harmonics-free.tcd:/usr/local/share/xti
de/harmonics-nonfree.tcd

       Alternately, make sure that they are by themselves in a special
       directory and specify that directory as the value of HFILE_PATH.
       If an element of HFILE_PATH is a directory, XTide will attempt to
       load every file in that directory (so be sure that they are all
       harmonics files!)
       If you are installing as root, then it is recommended that you add
       this definition to a system-wide script such as /etc/profile if you
       have one.
    2. The other way is by creating the file /etc/xtide.conf.  The
       environment variable, if set, takes precedence over the config
       file.
       If a configuration file is used, the first line should consist of
       the value that would be assigned to HFILE_PATH:
/usr/local/share/xtide/harmonics-free.tcd:/usr/local/share/xtide/harmonics-nonfr
ee.tcd

    II.  Specify the location of the World Vector Shoreline files (optional)

   Either set the environment variable WVS_DIR to the name of that
   directory or supply the directory name as the second line of the
   configuration file /etc/xtide.conf.

    III.  Run the configure script

bash-3.1$ ./configure

   XTide 2.9 is packaged with the popular and portable [19]GNU automake,
   so all usual GNU tricks should work.  Help on configuration options can
   be found in the CONFIGURE-HELP file or obtained by entering ./configure
   --help.

   The web server xttpd is not necessary to use tide or xtide, so most
   users needn't worry about it.  However, if you plan to run it, there is
   additional configuration at this point.

   To change the user and/or group under which xttpd tries to run (the
   defaults are nobody/nobody), provide the options --with-xttpd-user=user
   and/or --with-xttpd-group=group to configure.  If you want to run xttpd
   but you don't have root, you will have to set these to your own
   username and the name of some group to which you belong.

bash-3.1$ ./configure --with-xttpd-user=xttpd --with-xttpd-group==scarydmons

   You can also set the webmaster address for xttpd this way.

bash-3.1$ ./configure --with-webmaster="somebody@somewehere.else"

    IV.  Other optional and alternative configurables

   --enable-time-workaround Work around Y2038 problem; disable time
   zones.  See [20]Appendix A -- Historical predictions and Y2038
   compliance.
   --enable-gnu-attributes Use with g++ -Wall -Wextra to make warnings
   smarter.
   --enable-semicolon-pathsep Use ; instead of : to separate names in
   HFILE_PATH (good idea if they begin with C:\)
   --enable-local-files Locate xtide.conf, .xtide.xml, and
   .disableXTidedisclaimer files in current working directory

   You can change the compile-time defaults (colors, etc.) set in
   config.hh if you so choose.  However, the easiest way to set all of
   those things is with the [21]control panel in the interactive XTide
   program.

   The e-mail address for feedback in xttpd can also be changed by setting
   the environment variable XTTPD_FEEDBACK, in lieu of the configure
   option mentioned above.

  Compiling

bash-3.1$ make
bash-3.1$ su
bash-3.1# make install

Special cases

  Don't have X11

   If you don't have any version of X11 installed and just want to compile
   xttpd or tide, generate a Makefile using ./configure and then type
   'make xttpd' or 'make tide'.  You will probably need to install the
   binaries by hand.

  CPU-bound platform

   If running on the minimum recommended hardware (166 MHz Pentium PC) it
   is advisable to forego installing the [22]World Vector Shoreline
   database.  If a true color display is present, graph drawing can be
   sped up enormously by turning off anti-aliasing (see [23]settings,
   XTide*antialias).

  Cygwin

  XTide can be compiled and run using [24]Cygwin, which is an emulated Unix
  environment for Windows that is free for typical non-commercial users.  The
  Cygwin distribution and its full license terms are available from
  [25]http://www.cygwin.com/.

  Cygwin packages are all versioned separately, so there is no baseline "Cygwin
  version" against which to test XTide.  Testing was most recently performed
  with XTide 2.9.2 using the collection of packages that was current as of
  2007-03-31.

  As of then, the quirks apparent after brief testing were as follows.

    1. If only building certain of the programs, you must type (e.g.)
       'make tide.exe' instead of 'make tide'.  'make tide' causes the
       automake-generated makefile to do something silly.
    2. Graph drawing in the interactive interface is an order of magnitude
       slower.  The slowdown can be mitigated by turning off anti-aliasing
       (see [26]settings, XTide*antialias).
    3. When you drag a window around, fine-grained exposure events for any
       overlapped windows are queued but not delivered until you drop it.
       The resulting redraw behavior is suboptimal.
    4. When you resize a graph window, instead of delivering one
       ConfigureNotify event, Cygwin delivers a huge pile forming a
       continuum between the old size and the new one.^[27]1  This is
       worse than suboptimal as it can take a long time to resize the
       graph that many times.  Once again, the slowdown can be mitigated
       by turning off anti-aliasing (see [28]settings, XTide*antialias).

   Cygwin used to have worse problems than that, so it is highly advisable
   to update your installation before compiling XTide.

  Mac OS X

  XTide version 2.9.5 or newer should compile cleanly and run under Mac OS
  10.3.3 or later.

  If the PNG package is installed via Fink ([29]http://fink.sourceforge.net/),
  use CPPFLAGS="-I/sw/include" and LDFLAGS="-L/sw/lib" to find the
  Fink-installed PNG files.

  A [30]native port to OS X is also available.
  IRIX

  Some SGI machines come with a broken make program.  Use GNU make.
  HP-UX

  Long ago, a user submitted the following flags to get XTide to compile using
  the aCC compiler under HP-UX.  If somebody still uses this platform and the
  flags are still needed, they can be supplied to configure:

bash-3.1$ CXX="aCC" CXXFLAGS="-Wc,-koenig_lookup,on +DAportable" LDFLAGS="-lPW"
./configure

   It is possible that the latest configuration scripts add all needed
   flags automatically, but they have not been tested under HP-UX.

  Visual C++ Express Edition

  A native Windows binary for the command-line client tide can be built using
  Visual C++ Express Edition (either 2005 or 2008).  However, you will still
  need a [31]Cygwin environment to run the build process.  GCC is not required,
  but you'll need the bash shell, GNU make, etc.

  Visual C++ ignores most of the standard command-line switches that the build
  process tries to use.  These instructions include a minimal set of workarounds
  so that tide will compile anyway.  However, because of the basic
  incompatibilities, you will still get a lot of warnings.

  Before attempting to run configure or make, the environment variables PATH,
  INCLUDE, and LIB must be set to cover (A) the Visual C++ environment itself
  and (B) your installations of [32]libpng, [33]zlib and [34]libtcd native
  Windows libraries.

  To set variables for Visual C++, Visual C++ provides a batch file called
  vsvars32.bat that can be found somewhere in the Visual C++ program folder
  (e.g., C:\Program Files\Microsoft Visual Studio
  9.0\Common7\Tools\vsvars32.bat).  To get these settings into the Cygwin
  environment, follow these three steps:

    1. Start a Command Prompt (Start->Accessories->Command Prompt or run
       cmd.exe).
    2. At the command prompt, invoke vsvars32.bat (use Search to find it
       if necessary).
    3. At the command prompt, invoke cygwin.bat (use Search to find it if
       necessary).

   At that point you should have a bash prompt, and Visual C++ should
   work.  You can add the directories for your [35]libpng, [36]zlib and
   [37]libtcd library installations using bash commands, e.g.,

export LIB="${LIB};C:\\FunkyLibs\\lib"
export INCLUDE="${INCLUDE};C:\\FunkyLibs\\include"

   Having done that, run the configure script like this:

bash-3.1$ ./configure CC=cl CXX=cl LD=cl CPP="cl /E" LDFLAGS="zdll.lib libpng.li
b libtcd.lib" --enable-semicolon-pathsep --enable-local-files

   Depending on how you compiled your [38]libpng, [39]zlib and [40]libtcd
   libraries, the specific file names to be listed in LDFLAGS may be
   different.

   If you get a pop-up saying that "conftest.exe has encountered a
   problem," keep clicking on "Don't Send" until configuration proceeds.
   Then run 'make tide.exe'.  You will get a lot of warnings.  The
   resulting executable might not work from the Cygwin bash prompt but it
   should work when run from a Windows command prompt (DOS box).

   In accordance with the selected configure options, the following
   behaviors will differ from the default Unix behaviors:

     * File names in the environment variable HFILE_PATH or the
       configuration file xtide.conf should be separated by semicolons
       instead of colons.
     * The file xtide.conf (and any other configuration files that you
       use) should go in the current working directory.

   So for example you could put the following in an xtide.conf file in the
   current working directory:

C:\Documents and Settings\Mumble\Foo\harmonics-free.tcd;C:\Documents and Setting
s\Mumble\Foo\harmonics-nonfree.tcd

Troubleshooting

Q: Trying to compile tide using Visual C++, the configure script complains that
it can't find a library, and the following error messages appear in config.log.
Alternately, these errors can occur when linking tide.exe.

MSVCRT.lib(MSVCR80.dll) : error LNK2005: _malloc already defined in LIBCMT.lib(m
alloc.obj)
MSVCRT.lib(MSVCR80.dll) : error LNK2005: _free already defined in LIBCMT.lib(fre
e.obj)
LINK : warning LNK4098: defaultlib 'MSVCRT' conflicts with use of other libs; us
e /NODEFAULTLIB:library
conftest.exe : fatal error LNK1169: one or more multiply defined symbols found

   A: These errors occur when libraries are compiled with conflicting
   settings of the Visual C++ compiler switches /MT, /MD and /LD.  Try
   recompiling the libraries without using any such switches.

   Q: tide.exe compiles and runs with Visual C++ 2003, but non-ASCII
   characters (degrees symbol, accented characters, etc.) are not output
   correctly.

   A: This is why Visual C++ 2003 is unsupported.  The function that is
   needed to select a codeset other than the default MS-DOS legacy codeset
   does not work.  Use 2005 or 2008 instead.

   Q: Trying to compile XTide 2.9.4 or earlier on a Mac or Windows file
   system, the configure script crashes immediately.

   A: This is fixed in XTide 2.9.5.  XTide 2.9.4 and earlier did not
   anticipate case-insensitive file systems..

   Q: XTide compiles, but when I try to run it I get an error like
error while loading shared libraries: libtcd.so.0: cannot open shared object fil
e: No such file or directory

   A: Somehow, g++ found the shared library but your dynamic linker
   didn't.  To get the dynamic linker to find the library, you can just
   add its directory to the environment variable LD_LIBRARY_PATH.  For
   example, if you find the library in /usr/local/lib, you would add this
   to your .bashrc (if using bash):
export LD_LIBRARY_PATH=/usr/local/lib

   Or you would add this to your .cshrc (if using csh or tcsh):
setenv LD_LIBRARY_PATH /usr/local/lib

   Q: Trying to compile XTide 2.9.3 using Sun compilers, the following
   error occurs:
"/opt/SUNWspro/prod/include/CC/Cstd/./map", line 251: Error: Multiple declaratio
n for std::map<const Dstr, Configurable, std::less<const Dstr>, std::allocator<s
td::pair<const Dstr, Configurable>>>::insert(const std::pair<const Dstr, Configu
rable>&).
"BetterMap.hh", line 28:     Where: While specializing "std::map<const Dstr, Con
figurable, std::less<const Dstr>, std::allocator<std::pair<const Dstr, Configura
ble>>>".
"BetterMap.hh", line 28:     Where: Specialized in BetterMap<const Dstr, Configu
rable>.
"Settings.hh", line 30:     Where: Specialized in non-template code.

   A: This problem was reported on 2007-04-30 but the cause is still under
   investigation.  One can work around by compiling with g++ instead, but
   if this error is attributable to non-compliant C++ code in XTide I
   would like to fix it.  I do not personally have access to a Solaris
   platform to debug this, so please e-mail any relevant information or
   patches.

   Q: XTide 2.8.3 or earlier compiles, but when run the following error
   occurs:
X Error of failed request:  BadName (named color or font does not exist)
  Major opcode of failed request:  45 (X_OpenFont)

   A: You need to install the Schumacher fonts.  These fonts were reliably
   present on every X11 installation until 2006, when Linux distributions
   started breaking fonts out into lots of separate packages in accordance
   with upstream advice.  For what it's worth, XTide 2.9 gives a more
   helpful error message that tells you which font it could not load.

   Q: When compiling XTide, I get an error involving xml-something or
   lex.xml.c.

   A: For XTide 2.9 or later, do make xmlclean and then try again.  For
   XTide 2.8.3 or earlier, run the script do_xml.sh and then try again.
     __________________________________________________________________

   [41]<- Previous [42]-> Next [43]Contents

   ^1 The Xlib Programming Manual says the ConfigureNotify event is to be
   generated when the resize request "actually completes."  Unlike Expose
   events, there is no mechanism for handling consecutive ConfigureNotify
   events as a batch.  This suggests that the Cygwin interpretation is not
   what was intended.

References

   1. http://www.flaterco.com/xtide/sysreq.html
   2. http://www.flaterco.com/xtide/ports.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/files.html
   6. http://fedora.redhat.com/
   7. http://www.debian.org/
   8. http://www.gnu.org/software/automake/automake.html
   9. ftp://ftp.x.org/contrib/libraries/
  10. http://www.libpng.org/pub/png/libpng.html
  11. http://www.zlib.net/
  12. http://www.flaterco.com/xtide/files.html#libtcd
  13. http://www.flaterco.com/util/index.html
  14. http://www.flaterco.com/xtide/files.html#xtide
  15. http://www.flaterco.com/xtide/files.html#harmonicsfiles
  16. http://www.flaterco.com/xtide/files.html#WVS
  17. http://www.bzip.org/
  18. http://www.7-zip.org/
  19. http://www.gnu.org/software/automake/automake.html
  20. http://www.flaterco.com/xtide/time_t.html
  21. http://www.flaterco.com/xtide/advanced.html#cp
  22. http://www.flaterco.com/xtide/installation.html#WVS
  23. http://www.flaterco.com/xtide/settings.html#antialias
  24. http://www.cygwin.com/
  25. http://www.cygwin.com/
  26. http://www.flaterco.com/xtide/settings.html#antialias
  27. http://www.flaterco.com/xtide/installation.html#fn1
  28. http://www.flaterco.com/xtide/settings.html#antialias
  29. http://fink.sourceforge.net/
  30. http://www.flaterco.com/xtide/ports.html#Mac
  31. http://www.cygwin.com/
  32. http://www.libpng.org/pub/png/libpng.html
  33. http://www.zlib.net/
  34. http://www.flaterco.com/xtide/files.html#libtcd
  35. http://www.libpng.org/pub/png/libpng.html
  36. http://www.zlib.net/
  37. http://www.flaterco.com/xtide/files.html#libtcd
  38. http://www.libpng.org/pub/png/libpng.html
  39. http://www.zlib.net/
  40. http://www.flaterco.com/xtide/files.html#libtcd
  41. http://www.flaterco.com/xtide/sysreq.html
  42. http://www.flaterco.com/xtide/ports.html
  43. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Bridge Street

Available ports (and non-ports) for unsupported platforms

   If a program is derived from XTide source code, I call it a port.  If a
   program contains no XTide source code but can use the same harmonics
   files that some version of XTide did, I call it a non-port.  These are
   only listed if there is no good port to a given platform.  This is not
   an attempt to track all tide-predicting software, only that with some
   commonality with XTide.  Better software having nothing to do with
   XTide may be available, but is not listed here.

   These programs are all maintained by different people.  They may be
   significantly different from XTide 2 as documented here.  If you have
   problems with a port or non-port, please contact the correct
   maintainer.  I cannot help with anything but the canonical Unix
   distribution.

  Microsoft Windows

   XTide can be compiled and run using [5]Cygwin, which is an emulated
   Unix environment for Windows that is free for typical non-commercial
   users.  The Cygwin distribution and its full license terms are
   available from [6]http://www.cygwin.com/.  Please refer to the
   [7]Installation section for special instructions about using XTide
   under Cygwin.

   A native Windows binary for the command-line client tide can be built
   using Visual C++ 2008 Express Edition.  However, you still need a
   [8]Cygwin environment to run the build process.  See the
   [9]Installation section for details.

   The latest "native" port of the interactive client to Windows,
   [10]WTides by Phil Thornton, is based on XTide 2 but contains
   significant enhancements.  A "nagware" binary is available for
   downloading; sources are available for a fee.

   Caution:  There have been several accusations that Mr. Thornton is
   violating the GNU General Public License and even some ire directed at
   me for having linked to his site.  Firstly, please note that a link is
   not an endorsement.  Secondly, the requirement for "equivalent access"
   to source code that is in [11]GPLv3 was ambiguous in [12]GPLv2, which
   was the license in effect at the time that Mr. Thornton built his port.

   There are two older "native" ports to Microsoft Windows, distributed
   with both sources and binary:
     * The newer older port, "WXTide32" by Mike Hopper, is based on XTide
       1.6.2 but includes its own location chooser.  It works under
       Windows 95 or Windows NT.  It has a web page at
       [13]http://www.wxtide32.com/.
     * The older older port, "WTide16" and "WTide32" by Paul C. Roberts,
       was originally based on XTide 1.3 but may have been updated
       somewhat.  It works under Windows 3.1 or Windows 95.  It can be
       found at [14]ftp://ftp.demon.co.uk/pub/ibmpc/win3/apps/wtide.

  Mac

   XTide should compile cleanly and run under Mac OS 10.3.3 or later.  See
   the [15]installation instructions for details.

   Lee Ann Rucker has done a nativized port to OS X using [16]Cocoa and
   Objective-C.  It is available at
   [17]http://homepage.mac.com/lrucker/XTide/.

   For some earlier versions of Mac OS, there is a GPL'd non-port called
   Mr. Tides that you can find at
   [18]http://homepage.mac.com/augusth/MrTides/index.html.

  Palm

   Palm

   [19]Walt Bilofsky has implemented [20]Tide Tool for the Palm Pilot or
   any other compatible device running PalmOS.  Judging from the picture
   it does produce output comparable to that of XTide.

   Bilofsky writes: "Tide Tool used to qualify as a port, and still has a
   modest amount of code from XTide 1.5.  But since Jeff Dairiki redid the
   algorithm to use integer math, I'm not sure how much of it is XTide any
   more.  I guess I'd call it the descendant of a port."

  Pocket PC / Windows CE

   PocketPC

   Dave Buchholz has implemented [21]cTide for the PocketPC 2000 or
   PocketPC 2002.  It's a port of a port ([22]WXTide32), but the
   screenshots still look a lot like XTide.  You can find it at
   [23]http://airtaxi.net/ctide/.

  Timex Datalink USB

   Timex Datalink with DTide

   Paulo Marques has implemented DTide for the Timex Datalink USB
   wristwatch.  It uses a patched version of WXTide32 on the PC to allow
   the user to select locations and prepare simplified harmonics data to
   feed the application on the watch.  It can store more than 200
   (simplified) locations in the watch's memory.  The application on the
   watch is an assembly language non-port using only integer math.

   To get the application, download TreeBrowser_vX.zip and Tree Browser
   Feeders/DTide.zip from the Files > WristApps archive of Yahoo Group
   [24]timexdatalinkusb.

   To get the source (TreeBrowser asm and patch against WXTide32),
   download TreeBrowser_src.zip and DTide_src.zip from the Files >
   WristApps archive of Yahoo Group [25]timexdatalinkusbdevelop.

  HP Calculator

   HP Calculator

   David MacCuish and Dennis Straley have done a similar-in-spirit
   non-port for HP48G and HP49G series calculators.  As of 2001-11-08,
   [26]HpTide is still in development, but it now supports a larger number
   of locations.  For current news and status, please see the HpTide web
   site, [27]http://heygus.2y.net/hptide.
     __________________________________________________________________

   [28]<- Previous [29]-> Next [30]Contents

References

   1. http://www.flaterco.com/xtide/installation.html
   2. http://www.flaterco.com/xtide/modes.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.cygwin.com/
   6. http://www.cygwin.com/
   7. http://www.flaterco.com/xtide/installation.html#cygwin
   8. http://www.cygwin.com/
   9. http://www.flaterco.com/xtide/installation.html#VC++
  10. http://www.wtides.com/
  11. http://www.flaterco.com/xtide/disclaimer.html
  12. http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
  13. http://www.wxtide32.com/
  14. ftp://ftp.demon.co.uk/pub/ibmpc/win3/apps/wtide/
  15. http://www.flaterco.com/xtide/installation.html#mac
  16. http://developer.apple.com/cocoa/
  17. http://homepage.mac.com/lrucker/XTide/
  18. http://homepage.mac.com/augusth/MrTides/index.html
  19. http://www.toolworks.com/bilofsky/
  20. http://www.toolworks.com/bilofsky/tidetool/
  21. http://airtaxi.net/ctide/
  22. http://www.wxtide32.com/
  23. http://airtaxi.net/ctide/
  24. http://tech.groups.yahoo.com/group/timexdatalinkusb/
  25. http://tech.groups.yahoo.com/group/timexdatalinkusbdevelop/
  26. http://heygus.2y.net/hptide
  27. http://heygus.2y.net/hptide
  28. http://www.flaterco.com/xtide/installation.html
  29. http://www.flaterco.com/xtide/modes.html
  30. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Morning in OC

Modes

   This page provides an overview of the kinds of things that XTide can
   do.  How to do them will be explained in the [5]next section.

  Graph mode

   San Francisco graph

   Graph mode gives you a plot of the water level (or water velocity, in
   the case of currents) versus time.  The times of high and low tide (or
   max flood and max ebb) are printed across the top.  Sunrise and sunset
   are denoted with different background colors; moonrise, moonset, and
   moon phases are shown along the bottom.  A + mark on the graph
   indicates the conditions at the time that the graph was generated.

   For currents, the times of [6]slack water are also shown along the
   bottom.  If necessary, crowding of the bottom caption line can be
   relieved in several ways (see [7]Advanced usage).

   San Francisco Current graph

  Clock mode

   Clock mode

   Clock mode is similar to graph mode, but the captions are different and
   the window is automatically updated once a minute to show the latest
   conditions.  From top to bottom, the window shows the current time, the
   next high tide (or maximum flood), the predicted height or velocity for
   the current time (shown with a +), and the next low tide (or maximum
   ebb).  Other events like slack water and moon phases do not appear.

   Classic analog tide clock If a tide clock is iconified using an ancient
   window manager like twm, the icon will appear as a classic round tide
   clock that gives a vague idea of where you are in the tide cycle.
   Unfortunately, this feature is not accessible at all from newer windows
   environments that disregard the old icon protocol.  Even some of the
   old window managers had trouble with it; they would crash, or the icon
   would fail to update.

  Plain mode

   Plain text listing of events, no foo-foo.
San Francisco, California
37.8067 N, 122.4650 W

2003-02-13  2:17 PM PST   Moonrise
2003-02-13  3:25 PM PST  -0.32 feet  Low Tide
2003-02-13  5:46 PM PST   Sunset
2003-02-13 10:49 PM PST   4.64 feet  High Tide
2003-02-14  3:05 AM PST   3.16 feet  Low Tide
2003-02-14  5:44 AM PST   Moonset
2003-02-14  7:01 AM PST   Sunrise
2003-02-14  9:02 AM PST   6.27 feet  High Tide

  Calendar mode

   Calendar mode arranges most of the information available in text mode
   into a commonly used tabular layout.

                                January 2007

   Day High
   Low High
   Low High
   Phase Sunrise Sunset Moonrise Moonset
   Mon 01 3:48 AM EST 0.17 m 9:58 AM EST -0.14 m 5:07 PM EST 0.43 m 7:26
   AM EST 4:53 PM EST 2:49 PM EST 5:49 AM EST
   Tue 02 12:25 AM EST -0.01 m 4:46 AM EST 0.16 m 10:52 AM EST -0.14 m
   6:00 PM EST 0.42 m 7:26 AM EST 4:54 PM EST 3:48 PM EST 6:54 AM EST
   Wed 03 1:15 AM EST -0.01 m 5:40 AM EST 0.17 m 11:45 AM EST -0.14 m 6:50
   PM EST 0.41 m Full Moon 7:26 AM EST 4:55 PM EST 4:54 PM EST 7:49 AM EST
   Thu 04 2:00 AM EST -0.01 m 6:32 AM EST 0.18 m 12:37 PM EST -0.13 m 7:37
   PM EST 0.39 m 7:26 AM EST 4:56 PM EST 6:03 PM EST 8:34 AM EST
   Fri 05 2:42 AM EST -0.00 m 7:20 AM EST 0.19 m 1:28 PM EST -0.12 m 8:21
   PM EST 0.37 m 7:26 AM EST 4:57 PM EST 7:10 PM EST 9:09 AM EST
   Sat 06 3:20 AM EST -0.00 m 8:08 AM EST 0.20 m 2:16 PM EST -0.10 m 9:02
   PM EST 0.35 m 7:26 AM EST 4:58 PM EST 8:15 PM EST 9:37 AM EST
   Sun 07 3:56 AM EST -0.00 m 8:56 AM EST 0.21 m 3:04 PM EST -0.08 m 9:40
   PM EST 0.32 m 7:26 AM EST 4:59 PM EST 9:17 PM EST 10:02 AM EST

   "Alt" calendar mode arranges the information into a traditional weekly
   calendar layout.

                     Sun 07     Mon 08 Tue 09 Wed 10 Thu 11 Fri 12 Sat 13
   Low Tide -0.00 m
   3:56 AM EST
   Sunrise
   7:26 AM EST
   High Tide 0.21 m
   8:56 AM EST
   Moonset
   10:02 AM EST
   Low Tide -0.08 m
   3:04 PM EST
   Sunset
   4:59 PM EST
   Moonrise
   9:17 PM EST
   High Tide 0.32 m
   9:40 PM EST Low Tide -0.01 m
   4:28 AM EST
   Sunrise
   7:26 AM EST
   High Tide 0.22 m
   9:46 AM EST
   Moonset
   10:23 AM EST
   Low Tide -0.05 m
   3:53 PM EST
   Sunset
   5:00 PM EST
   High Tide 0.30 m
   10:16 PM EST
   Moonrise
   10:17 PM EST Low Tide -0.02 m
   4:58 AM EST
   Sunrise
   7:26 AM EST
   High Tide 0.22 m
   10:39 AM EST
   Moonset
   10:43 AM EST
   Low Tide -0.01 m
   4:46 PM EST
   Sunset
   5:00 PM EST
   High Tide 0.27 m
   10:51 PM EST
   Moonrise
   11:16 PM EST Low Tide -0.04 m
   5:28 AM EST
   Sunrise
   7:25 AM EST
   Moonset
   11:03 AM EST
   High Tide 0.24 m
   11:35 AM EST
   Sunset
   5:01 PM EST
   Low Tide 0.03 m
   5:49 PM EST
   High Tide 0.24 m
   11:27 PM EST Moonrise
   12:14 AM EST
   Low Tide -0.06 m
   6:00 AM EST
   Sunrise
   7:25 AM EST
   Last Quarter
   7:45 AM EST
   Moonset
   11:23 AM EST
   High Tide 0.25 m
   12:32 PM EST
   Sunset
   5:02 PM EST
   Low Tide 0.05 m
   7:01 PM EST High Tide 0.21 m
   12:07 AM EST
   Moonrise
   1:15 AM EST
   Low Tide -0.08 m
   6:35 AM EST
   Sunrise
   7:25 AM EST
   Moonset
   11:46 AM EST
   High Tide 0.28 m
   1:29 PM EST
   Sunset
   5:04 PM EST
   Low Tide 0.06 m
   8:18 PM EST High Tide 0.18 m
   12:52 AM EST
   Moonrise
   2:17 AM EST
   Low Tide -0.09 m
   7:15 AM EST
   Sunrise
   7:25 AM EST
   Moonset
   12:14 PM EST
   High Tide 0.30 m
   2:22 PM EST
   Sunset
   5:05 PM EST
   Low Tide 0.06 m
   9:30 PM EST

   Calendar mode is not available from the interactive client.

  Banner mode

   Banner mode is a specialization of graph mode for output on old tractor
   feed dot matrix or line printers that use continuous reams of paper.
   Also useful as a workaround if your printing application does stupid
   things with color graphs.  The graph is turned sideways and the aspect
   ratio is adjusted for Pica type.  This mode is only available in the
   command line client.
San Francisco, San Francisco Bay, California
37.8067 N, 122.4650 W

-11****-****-****-***********************
*******3****2****1****0*****1****2****3    4    5    6    7     8    9
******* **** **** **** ***** **** **
-12****f****f****f****f*****f****f    f    f    f    f    f     f    f
*******t****t****t****t*****t**  t    t    t    t    t    t     t    t
*****************************
**************************+ |    |    |    |    |    |    |     |    |
-1************************  |    |    |    |    |    |    |     |    |
****Moonrise************    |    |    |    |    |    |    |     |    |
-***1:55 PM PST********     |    |    |    |    |    |    |     |    |
-2*********************     |    |    |    |    |    |    |     |    |
**********************|     |    |    |    |    |    |    |     |    2007-02-27
**********************|     |    |    |    |    |    |    |     |   2:56 PM PST
-3********************|     |    |    |    |    |    |    |     |    |
**********************|     |    |    |    |    |    |    |     |    |
***********************     |    |    |    |    |    |    |     |    |
-4*********************     |    |    |    |    |    |    |     |    |
************************    |    |    |    |    |    |    |     |    |
*************************   |    |    |    |    |    |    |     |    |
-5************************* |    |    |    |    |    |    |     |    |
****************************|    |    |    |    |    |    |     |    |
******************************   |    |    |    |    |    |     |    |
-6******************************||||||||
**********************************|||||||
***********************************|||||||
-7***********************************|||||||
***************************************||||||
*****************************************||||||
-8*****************************************||||||
*********************************************|||||
**********************************************|||||
-9*********************************************|||||
************************************************|||||
*************************************************|||2007-02-27
-10**********************************************|||10:06 PM PST
*************************************************||||
************************************************|||||
-11*********************************************|||||
***********************************************|||||
-*********************************************|||||
-12******************************************|||||
-******************************************||||||
******************************************||||||
-1***************************************||||||
****************************************||||||
***************************************||||||
-2*************************************||||||
**************************************||||||2007-02-28
**************************************||||||2:45 AM PST
-3************************************|||||||
**************************************|||||||

  Stats mode

   Stats mode is mainly for finding the highest high tide and lowest low
   tide within some period of time.  However, it also provides an
   estimation of the Mean Lower Low Water datum based on the generated
   predictions.  In cases where an authoritative benchmark for a station
   is not available, this can be used to derive a reasonable
   approximation.  If the datum for the station has already been set to
   MLLW (as it should have been, for all U.S. stations) then the estimated
   value should be close to zero.

   Stats mode is only available in the command line client.
Bar Harbor, Frenchman Bay, Maine
44.3917 N, 68.2050 W

Mathematical upper bound:  15.21 feet
Mathematical lower bound:  -3.87 feet
Mathematical mean, assuming symmetry:   5.67 feet

Searched interval from 2007-01-01 12:00 AM EST to 2008-01-01 12:00 AM EST
Maximum was  13.44 feet at 2007-11-25 10:31 AM EST
Minimum was  -2.05 feet at 2007-04-18  5:53 AM EDT
Mean of maxima and minima was   5.67 feet
Estimated MLLW:   0.15 feet

CPU time used:  0.167974 s

  Raw mode

   Raw mode is for getting machine-readable output that can be fed into
   other Unix programs.  The first column is a Unix time_t timestamp
   (seconds since 1970-01-01 00:00Z); the second column is tide heights in
   whatever units were selected for the location.
896624777 0.180580
896628377 1.271889
896631977 3.463100
896635577 6.084148
896639177 8.402840
896642777 9.943272
896646377 10.421064
896649977 9.672793
896653577 7.856022
896657177 5.543402
896660777 3.413487
896664377 1.926805
896667977 1.371479

  Medium rare mode

   Medium rare mode is just like raw mode except that the timestamps are
   "cooked" according to the date and time format settings that are in
   effect.
2002-02-06  4:56 PM EST 2.054437
2002-02-06  5:56 PM EST 1.573781
2002-02-06  6:56 PM EST 1.086896
2002-02-06  7:56 PM EST 0.656111
2002-02-06  8:56 PM EST 0.224729
2002-02-06  9:56 PM EST -0.161049
2002-02-06 10:56 PM EST -0.265521
2002-02-06 11:56 PM EST 0.077530

  List mode

   List mode does not provide tide predictions at all.  It is simply a way
   to get the list of supported locations from the command line client.

   The 'Type' column shows Ref for reference stations and Sub for
   subordinate stations.  [8]You should care about the difference.

   Location Type Coordinates
   0.8 n.mi. above entrance, Alloway Creek, New Jersey Sub 39.4967 N,
   75.5167 W
   130th Street, Hudson River, New York Sub 40.8167 N, 73.9667 W
   2.5 miles above mouth, Little Satilla River, Georgia Sub 31.0583 N,
   81.4933 W
   2.5 n.mi. above entrance, Alloway Creek, New Jersey Sub 39.5050 N,
   75.4833 W
   3 miles above A1A highway bridge, Loxahatchee River, Florida Sub
   26.9700 N, 80.1267 W
   37th Avenue, Long Island City, East River, New York, New York Sub
   40.7617 N, 73.9467 W

  About mode

   About mode does not provide tide predictions either.  Instead, it shows
   the metadata for a station ("About this station").

   Name
Eastport, Passamaquoddy Bay, ME

   In file
harmonics-dwf-2004-10-18-v2.tcd

   Station ID context
NOS

   Station ID
8410140

   Date imported
2004-09-01

   Coordinates
44.9033 N, 66.9850 W

   Country
U.S.A.

   Time zone
:America/New_York

   Source
http://tidesandcurrents.noaa.gov/

   Restriction
Public domain

   Comments
Harmonic constants from web snapshot taken 2004-08-26
Datum from benchmark sheet, publication date 2003-04-21

   Type
Reference station, tide

   Meridian
0:00

   Datum
Mean Lower Low Water

   Native units
meters

   Confidence
10

Formats

   XTide can render output in seven different formats:  X-windows, HTML,
   LaTeX, iCalendar, PNG, CSV, or text.  The X-windows format is implicit
   in the interactive client and can't be selected explicitly.  The others
   can be selected in the non-interactive client and are invoked
   automatically by the the interactive and web clients (e.g., when you
   save output to a file).

   The currently supported combinations of mode and format are as follows:

         Mode                 Legal forms
     about         text, HTML, X-windows
     banner        text
     calendar      text, HTML, LaTeX, iCalendar, CSV
     alt. calendar text, HTML, LaTeX
     clock         PNG, X-windows
     graph         text, PNG, X-windows
     list          text, HTML
     plain         text, X-windows, CSV
     raw           text, X-windows, CSV
     medium rare   text, X-windows, CSV
     stats         text

   The HTML and PNG formats are adequately demonstrated by the examples
   above in the Modes section.

  Text format

   Several of the preceding examples, like plain mode, were in text
   format.  Here is an example of graph mode using the text format:
San Francisco, San Francisco Bay, California            
-122003-02-132003-02-13                 2003-02-13     
 PST2:18 AM PST8:12 AM PST                3:25 PM PST    
                                         
                                         
                                         
                                         
2 m---------------------------------------------------------------------------
*************                               
******************                             
***************************                           
*****************************************                         
1 m***********************************************-----------------------------
****************************************************                     *
******************************************************                   ***
********************************************************                 ******
**********************************************************            *********
0 m****************************************************************************
*******************************************************************************
*******************************************************************************
********************Moonset****************************Moonrise****************
******************4:51 AM PST*************************2:17 PM PST**************
1**12***1***2***3**4***5***6***7***8***9*10**11**12***1***2***3***4**5***6***7*
|**|||**|***|***|**|***|***|***|***|***|**|***|***|***|***||**|***|**|***|***|*

   Calendar mode is kind of cramped in text format if you use all default
   settings, but it can be made to work by using a compact time format,
   setting a wider TTY width, and/or turning off sun and moon
   information.  These are [9]settings that you can change with the
   [10]control panel or [11]command-line switches.  See [12]Appendix C for
   related discussion.
Bar Harbor, Frenchman Bay, Maine
44.3917 N, 68.2050 W

                                   May 2006

Day    High   Low    High   Low    High   Phase  Sunris Sunset Moonri Moonse
Mon 01 01:42  08:10  14:23  20:23                05:23  19:36  07:38
Tue 02 02:32  09:02  15:16  21:16                05:22  19:37  08:38  00:32
Wed 03 03:25  09:56  16:10  22:12                05:20  19:39  09:44  01:17
Thu 04 04:21  10:52  17:07  23:12                05:19  19:40  10:51  01:52
Fri 05 05:20  11:49  18:05                First  05:18  19:41  11:58  02:19
Sat 06        00:13  06:20  12:45  19:01         05:16  19:42  13:03  02:40
Sun 07        01:11  07:18  13:38  19:52         05:15  19:44  14:07  02:59
Mon 08        02:06  08:12  14:26  20:39         05:14  19:45  15:10  03:15
Tue 09        02:55  09:01  15:10  21:21         05:12  19:46  16:14  03:31
Wed 10        03:39  09:46  15:51  21:59         05:11  19:47  17:19  03:47
Thu 11        04:21  10:27  16:28  22:36         05:10  19:48  18:27  04:05
Fri 12        04:59  11:06  17:05  23:11         05:09  19:49  19:38  04:26
Sat 13        05:36  11:45  17:41  23:48  Full M 05:07  19:51  20:51  04:52
Sun 14        06:15  12:24  18:19                05:06  19:52  22:02  05:26
Mon 15 00:26  06:55  13:05  18:59                05:05  19:53  23:07  06:11
Tue 16 01:08  07:38  13:49  19:44                05:04  19:54         07:08
Wed 17 01:55  08:25  14:38  20:35                05:03  19:55  00:02  08:17
Thu 18 02:46  09:18  15:32  21:32                05:02  19:56  00:45  09:34
Fri 19 03:43  10:14  16:30  22:34                05:01  19:57  01:19  10:53
Sat 20 04:45  11:13  17:30  23:40         Last Q 05:00  19:58  01:46  12:12
Sun 21 05:50  12:14  18:31                       04:59  19:59  02:08  13:30
Mon 22        00:46  06:56  13:14  19:31         04:58  20:00  02:29  14:47
Tue 23        01:50  07:59  14:12  20:27         04:57  20:01  02:49  16:05
Wed 24        02:49  08:59  15:07  21:21         04:56  20:02  03:10  17:23
Thu 25        03:45  09:56  15:59  22:12         04:56  20:03  03:34  18:43
Fri 26        04:38  10:49  16:49  23:00         04:55  20:04  04:03  20:01
Sat 27        05:28  11:39  17:38  23:48  New Mo 04:54  20:05  04:40  21:15
Sun 28        06:16  12:27  18:25                04:53  20:06  05:26  22:18
Mon 29 00:34  07:03  13:15  19:13                04:53  20:07  06:23  23:09
Tue 30 01:21  07:51  14:03  20:01                04:52  20:08  07:27  23:49
Wed 31 02:09  08:38  14:51  20:50                04:52  20:09  08:35

  LaTeX format

   Running LaTeX formatted output through pdflatex yields a PDF that looks
   approximately [13]like this.  See [14]Appendix C for hints on obtaining
   the best results.

  iCalendar format

   The iCalendar format yields an .ics file that can be imported by
   standards-compliant calendar tools to put tide events on your
   schedule.  It is only useful in calendar mode.

  CSV format

   CSV stands for Comma-Separated Values, a.k.a. comma-delimited.  This
   rigid format is useful for importing XTide output into database and
   spreadsheet applications with fixed columns.  Commas that are part of
   field values are replaced by the pipe character (|).
Washington| D.C.,2004-03-04,3:40 PM EST,,Moonrise
Washington| D.C.,2004-03-04,6:04 PM EST,,Sunset
Washington| D.C.,2004-03-04,6:23 PM EST,2.75 ft,High Tide
Washington| D.C.,2004-03-05,1:30 AM EST,0.21 ft,Low Tide

   In calendar mode, the columns in CSV format are:  location name, date,
   five reps of (max time, max value), five reps of (min time, min value),
   ten reps of slack time, sunrise, sunset, moonrise, moonset.  The number
   of columns allocated is controlled by the compile-time constants
   numMaxMin and numRiseSet in CalendarFormC.cc.  Events exceeding the
   number of columns available are discarded with a warning.  Moon phases
   and mark level crossings are just discarded.

   The use of compile-time constants instead of dynamically adjusted
   values is intentional, since whatever application is reading the CSV
   output needs the interpretation of columns to be predictable.  However,
   the default configuration allowing one column for rise and set events
   is not always adequate.  Yes!  You can have two sunsets in one day, and
   you don't even need Daylight Savings Time to do it:
Isla Neny, Antarctica
68.2000 S, 67.0000 W

2001-01-24 12:03 AM ARST   Sunset
2001-01-24  3:17 AM ARST   Sunrise
2001-01-24 11:57 PM ARST   Sunset
     __________________________________________________________________

   [15]<- Previous [16]-> Next [17]Contents

References

   1. http://www.flaterco.com/xtide/ports.html
   2. http://www.flaterco.com/xtide/interactive.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/interactive.html
   6. http://www.flaterco.com/xtide/faq.html#240
   7. http://www.flaterco.com/xtide/advanced.html#crowding
   8. http://www.flaterco.com/xtide/faq.html#refsub
   9. http://www.flaterco.com/xtide/settings.html
  10. http://www.flaterco.com/xtide/advanced.html#cp
  11. http://www.flaterco.com/xtide/settings.html
  12. http://www.flaterco.com/xtide/pound_to_fit.html
  13. http://www.flaterco.com/xtide/BarHarbor.pdf
  14. http://www.flaterco.com/xtide/pound_to_fit.html
  15. http://www.flaterco.com/xtide/ports.html
  16. http://www.flaterco.com/xtide/interactive.html
  17. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Pemaquid bell

Using the interactive interface

   The first time you run xtide, you will get a license and disclaimer
   window.  Read it, then click "Don't show this again" and dismiss it.

   When XTide is finished indexing the harmonics files you will get a
   location chooser.  The location chooser initially shows a hemisphere of
   the globe.  The location list enumerates every tide station that is
   plotted on the map.  Buttons with labels such as "A-S" and "S-Z" will
   appear on the location list window if the list is too long to display
   all at once; use these buttons to switch between the different pieces
   of the list.

   (If you do not get outlines of coastlines, please refer to the
   [5]installation section regarding World Vector Shoreline files.)

   Globe window

   Location list window

   You can change to a flat map projection that shows the entire world at
   once by clicking on Flat.  You can make this your default location
   chooser if desired (see the later section [6]Customizing XTide).

   Map window

   You can zoom in on an area by clicking on the map with the left mouse
   button; zooming out is accomplished with the button at the bottom of
   the map window.  Your view can be shifted left, right, up, or down
   using the arrow keys on the keyboard.  The location list updates to
   contain only those tide stations that are visible.  You can cause the
   location list to include all available locations at once by clicking on
   List All.  This will also bring up locations whose coordinates are
   unknown.

   Instead of zooming, you can narrow the list to a small area by clicking
   on that area with the right mouse button.  A circle will be drawn on
   the map indicating the area selected:

   Map window with circle

   When you are ready to choose a location, you can either click on it in
   the location list or zoom down to it on the map and click on the
   appropriate red dot with the middle mouse button.  A tide graph for the
   selected location will then pop up.

   Graph window

   The Backward and Forward buttons allow you to move forward or backward
   in time by a small amount.  Pull down the Options menu to gain access
   to the Set Time option, which allows arbitrarily large adjustments.
   The Options menu also provides these other options:

   Option Function
   Save Export the contents of the window to a PNG or text file, as
   appropriate.  (In raw and medium rare modes, you are given the
   opportunity to adjust the start and end times for the output.)
   Set Mark See [7]next section.
   Convert ft<->m Convert units to the preferred system.
   Set Aspect See [8]next section.
   Set Step See [9]next section.
   New Graph Window Pop up a graph mode window for the location.
   New Plain Mode Window Pop up a plain mode window for the location.
   New Raw Mode Window Pop up a raw mode window for the location.
   New Medium Rare Mode Window Pop up a medium rare mode window for the
   location.
   New Clock Window Pop up a clock mode window for the location.
   About This Station Show station metadata.
   New Location Chooser Pop up a new location chooser.
   Control Panel See [10]next section.

   Without getting into the complicated options, you can navigate from the
   location chooser to a graph window to other modes for the same location
   as you see fit.  Use the Dismiss buttons to get rid of windows that you
   are through with.

   Text window

   Text windows provide Forward and Backward buttons for scrolling forward
   and backward in time, and they also provide the same Options menu that
   is available on graph windows.

   Note:  Starting with XTide 2.9, text windows support mouse wheel
   scrolling provided that the mouse wheel has been mapped to buttons 4
   and 5.  This mapping is typically configured in xorg.conf (Option
   "ZAxisMapping" "4 5").

   Clock window   Clock window with buttons

   By default, clock windows first appear with no buttons whatsoever,
   which is how you want them if you are going to leave them running on
   your desktop.  However, you can make the buttons appear and disappear
   by clicking anywhere on the graph inside of the clock window.

   The Options menu is again the same.  Forward and Backward buttons are
   not provided for the obvious reason.
     __________________________________________________________________

   [11]<- Previous [12]-> Next [13]Contents

References

   1. http://www.flaterco.com/xtide/modes.html
   2. http://www.flaterco.com/xtide/advanced.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/installation.html#WVS
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/advanced.html
   8. http://www.flaterco.com/xtide/advanced.html
   9. http://www.flaterco.com/xtide/advanced.html
  10. http://www.flaterco.com/xtide/advanced.html
  11. http://www.flaterco.com/xtide/modes.html
  12. http://www.flaterco.com/xtide/advanced.html
  13. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]The tide cometh, Provincetown, MA

Advanced usage

  Mark level

   The "mark level" is a specific tidal height or current velocity of your
   choosing.  When you set a mark level for a location, the times at which
   the tide level crosses the mark level will be displayed at the bottom
   of graphs and included in plain listings and calendars.  This option is
   useful to determine the times when the tide will be low enough to
   expose something that is submerged at high tide or high enough to
   provide a desired depth.  You can set a mark level by selecting the Set
   Mark option on the Options menu.  In the following example, a mark
   level of 1 m has been applied to Bar Harbor predictions to find the
   approximate time at which one can walk to Bar Island without getting
   one's feet wet.

   Bar Harbor with mark level

   Mark level crossings are not displayed in clock mode windows due to
   lack of space.

  Aspect

   The "aspect" is a number that controls how stretched out or scrunched
   up a graph is.  If timestamps are overlapping one another on a tide
   graph and becoming unreadable, you can increase the aspect to make them
   farther apart.  An aspect of 1.0 is "normal;" an aspect of 2.0
   stretches the graph by a factor of 2; an aspect of 0.5 does the
   opposite, compressing the graph.  You can change the aspect by
   selecting the Set Aspect option on the Options menu.

  Step

   In raw and medium rare modes, tide levels are normally listed with an
   increment of one hour for successive lines of output.  You can adjust
   this increment using the Set Step option.

  The control panel

  The control panel is the easiest way to customize the many user-serviceable
  [5]settings of XTide.  It's not pretty, but it gets the job done.

  XTide control panel

  Colors can be changed to any of the "standard" X-windows color names or to
  24-bit RGB specifications of the form rgb:hh/hh/hh by typing the new colors in
  the dialog boxes.  Other settings have pull-down choice menus or counting
  buttons to help you along.  Least user-friendly, but most powerful, are the
  timestamp formats.  In return for reading the Unix man page for the strftime
  library function, you are empowered to change the timestamp formats to
  practically anything you could ever need.

  You can choose Apply to see how the settings look in the current session only,
  or Save to make the settings permanent.  They will be saved in the file
  ~/.xtide.xml.
  Example 1:  Three ways to fix crowding of the bottom caption line

  Original graph with crowded caption line:

  San Francisco Current graph

  With aspect 1.25 (to stretch out the graph):

  San Francisco Current graph

  With time format "%H:%M" (to eliminate AM/PM and time zone verbiage):

  San Francisco Current graph

  With event mask "Mm" (to filter out moonrise and moonset events):

  San Francisco Current graph
  Example 2:  Two ways to fix missing depth axis

  This station has such a small tidal range that the only label on the depth
  axis is zero meters, which is kind of useless:

  Missing depth example

  With option to label tenths of units enabled:

  Missing depth example

  With preferred units set to feet:

  Missing depth example
  Command line options

  The interactive client supports all of the command line switches related to
  [6]settings which are described in a later section.  In addition, it supports
  the following.

   -b "YYYY-MM-DD HH:MM"
          With -l, specify the begin (start) time for predictions using
          the ISO 8601 compliant format YYYY-MM-DD HH:MM, where hours
          range from 00 to 23.  The timestamp is in the local time zone
          for the location, or in UTC if the -z setting is engaged.  If no
          -b is supplied, the current time will be used.  (Note [7]Quirk
          #1)

   -display "X display"
          Specify the X display, e.g. "quake:0.0".  This overrides the
          DISPLAY environment variable.

   -fn "font"
          Specify the font to use for text windows, buttons, and labels.
          This will not affect the font used in tide graphs and other
          cramped spaces, which is not a user-selectable parameter.

   -geometry "XOFFYOFF"
          Specify a position for the window corresponding to the first use
          of -l.  (Width and height are controlled by different
          [8]settings.)

   -l "Location Name"
          Specify a location for tide predictions.  When given to the
          interactive client, this causes it to start a tide clock for the
          specified location instead of launching a location chooser on
          startup.  This is useful for starting a tide clock automatically
          when you log on.  Multiple uses of -l will result in multiple
          tide clocks.

   -m a|g|m|p|r
          With -l, specify mode to be about, graph, medium rare, plain, or
          raw instead of clock.

   -v
          Print version string and exit.  Please note that versions marked
          as DEVELOPMENT versions are not really versioned; they are work
          in progress and will change without warning.

  If you use the same location a lot, you can set the environment variable
  XTIDE_DEFAULT_LOCATION to its name instead of using -l every time.

  Other switches that are supported by the [9]non-interactive interface are not
  supported by the interactive interface and will be ignored.

  The arguments to -display, -fn, and -geometry cannot be concatenated with the
  switches (see [10]Quirk #5).
    _________________________________________________________________________

  [11]<- Previous [12]-> Next [13]Contents

References

   1. http://www.flaterco.com/xtide/interactive.html
   2. http://www.flaterco.com/xtide/tty.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/settings.html
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/bugs.html
   8. http://www.flaterco.com/xtide/settings.html
   9. http://www.flaterco.com/xtide/tty.html
  10. http://www.flaterco.com/xtide/bugs.html
  11. http://www.flaterco.com/xtide/interactive.html
  12. http://www.flaterco.com/xtide/tty.html
  13. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Tide closes in

Using the command line interface

   The command line interface, tide, supports a number of [5]modes that
   cannot be accessed with the interactive client.  It can run without
   X-windows, and unlike the interactive client, it can easily be invoked
   from shell scripts.

   The minimal usage is simply to specify a location with -l.  The default
   mode is plain, and the default format is text:

$ tide -l "anchorage, al"
Anchorage, Alaska
61.2383 N, 149.8883 W

2003-02-12  7:27 AM AKST   Moonset
2003-02-12  8:50 AM AKST   Sunrise
2003-02-12 10:19 AM AKST  10.72 feet  Low Tide
2003-02-12 11:34 AM AKST   Moonrise
2003-02-12  3:42 PM AKST  24.41 feet  High Tide
2003-02-12  5:37 PM AKST   Sunset
2003-02-12 11:00 PM AKST   1.95 feet  Low Tide
2003-02-13  5:31 AM AKST  25.51 feet  High Tide
2003-02-13  8:29 AM AKST   Moonset

   If you use the same location a lot, you can set the environment
   variable XTIDE_DEFAULT_LOCATION to its name instead of using -l every
   time.

   The non-interactive client supports all of the command line switches
   related to [6]settings which are described in a later section.  In
   addition, it supports the following.

   -b "YYYY-MM-DD HH:MM"
          Specify the begin (start) time for predictions using the ISO
          8601 compliant format YYYY-MM-DD HH:MM, where hours range from
          00 to 23.  The timestamp is in the local time zone for the
          location, or in UTC if the -z setting is engaged.  If no -b is
          supplied, the current time will be used.  (Note [7]Quirk #1)

   -e "YYYY-MM-DD HH:MM"
          Specify the end (stop) time for predictions using the ISO 8601
          compliant format YYYY-MM-DD HH:MM, where hours range from 00 to
          23.  The timestamp is in the local time zone for the location,
          or in UTC if the -z setting is engaged.  If no -e is supplied,
          the end time will be set to four days after the begin time.
          (Note [8]Quirk #2)

   When it matters, -b and -e ranges mean specifically "all t such that b
   <= t < e."

   -f c|h|i|l|p|t
          Specify the output format as CSV, HTML, iCalendar, LaTeX, PNG,
          or text.  See the [9]modes page for legal modes and formats.
          The default is text.

   -l "Location Name"
          Specify a location for tide predictions.  You can use the -l
          switch more than once if you want to specify multiple locations.

   -m a|b|c|C|g|l|m|p|r|s
          Specify mode to be about, banner, calendar, alt. calendar,
          graph, list, medium rare, plain, raw, or stats.  See the
          [10]modes page for legal modes and formats.  The default is
          plain.

   -ml [-]N.NN(ft|m|kt)
          Specify the mark level to be used in predictions.  The
          predictions will include the times when the tide level crosses
          the mark.  Example usage: -ml -0.25ft

   -o "filename"
          Redirect output to the specified file (appends).

   -s "HH:MM"
          Specify the step interval, in hours and minutes, for raw or
          medium rare mode predictions.  The default is one hour.

   -v
          Print version string and exit.  Please note that versions marked
          as DEVELOPMENT versions are not really versioned; they are work
          in progress and will change without warning.

   The interactive interface does not support all of these switches and
   options.  For example, you can't pop up a graph with a mark line on it
   by saying xtide -m g -ml 1ft.  Refer to the [11]previous page for a
   list of the options supported by the interactive interface.

   Starting with version 2.6, XTide understands the following syntactic
   shortcuts:
     * Arguments can be concatenated with their switches.
     * A yes/no switch that omits its argument implies "y".
     * Using +xx instead of -xx for a yes/no switch inverts the argument
       (so if the argument is omitted, "n" is implied).

   Some shorthand forms are ambiguous.  For example, -lw5 could mean "set
   the line width to 5" (-lw 5) or it could mean "load the location named
   w5" (-l w5).  If this happens, you will get an error and will need to
   spell out what you meant.
     __________________________________________________________________

   [12]<- Previous [13]-> Next [14]Contents

References

   1. http://www.flaterco.com/xtide/advanced.html
   2. http://www.flaterco.com/xtide/xttpd.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/modes.html
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/bugs.html
   8. http://www.flaterco.com/xtide/bugs.html
   9. http://www.flaterco.com/xtide/modes.html
  10. http://www.flaterco.com/xtide/modes.html
  11. http://www.flaterco.com/xtide/advanced.html#intopts
  12. http://www.flaterco.com/xtide/advanced.html
  13. http://www.flaterco.com/xtide/xttpd.html
  14. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Nobska Light, Cape Cod, MA, 1998-06-17

Running the web server

   xttpd is an XTide web server.  It provides web-based access to XTide's
   tide predictions by allowing a web browser to speak directly to the
   XTide program in HTTP.  xttpd can replace httpd or it can co-exist with
   one.  Usage:  xttpd [port] [...other xtide [5]settings switches...].

   xttpd forks itself into the background and uses the syslog facility for
   all logging.  Hosts connecting to xttpd are logged with priority INFO.

   If you run xttpd with no command line arguments, it will assume that it
   is replacing httpd and try to bind port 80.  If you want it to co-exist
   with an existing server, or if you do not have privilege to get port
   80, give it the port number as the first command line argument:

% xttpd 8080

   You will then need to link it up as http://www.wherever.org:8080/
   instead of just http://www.wherever.org/, but otherwise, no damage
   done.  Similarly, if you wish to bind a specific address, you can
   specify that as the first argument:

% xttpd 127.0.0.2

   If you need to specify both address and port number, separate the two
   with a slash, like this:

% xttpd 127.0.0.2/8080

   Once the port is established, xttpd will try to set its UID and GID to
   values that were specified at compile time.  If it is unable to do
   this, it will log failure messages to syslog and then exit.
   Consequently, if it is to be started by someone other than root, that
   user's UID and GID must be configured at compile time.  Instructions
   for doing this are available at
   [6]http://www.flaterco.com/xtide/installation.html#xttpd.

   You can set the address for feedback either at compile time as
   described in the installation instructions or with the environment
   variable XTTPD_FEEDBACK.

   xttpd will produce a small number of zombie processes during normal
   operation.  They are cleaned up after each new connection, so there is
   no cause for concern.

   Since a web site is supposed to be self-explanatory, the process of
   using xttpd will not be documented here.  If there are problems with
   people not being able to figure out how to use it, these should be
   reported to me as bugs, and the explanatory text in the web server will
   be updated accordingly.

  Troubleshooting

  Q: When I run xttpd, it exits immediately with no errors to tell me what went
  wrong.

  A: When executed, xttpd immediately disassociates itself from your terminal
  and starts logging all diagnostics to syslog.  So look in your system logs.
  You will find these someplace like /var/log or /var/adm/log.
    _________________________________________________________________________

  [7]<- Previous [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/tty.html
   2. http://www.flaterco.com/xtide/settings.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/settings.html
   6. http://www.flaterco.com/xtide/installation.html#xttpd
   7. http://www.flaterco.com/xtide/tty.html
   8. http://www.flaterco.com/xtide/settings.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Girl feeding gulls

Customizing XTide

   XTide is customized by changing its settings.  The most convenient way
   to do this is generally through the control panel that is documented in
   a [5]previous section.  However, you can also change these settings in
   config.hh, in your X resources database, or on the command line.  The
   order of precedence, from least significant to most significant, is:
    1. config.hh
    2. Xdefaults (X resources)
    3. ~/.xtide.xml (control panel)
    4. command line

   Note that only xtide (not xttpd or tide) reads Xdefaults.

   Canonically, all command line settings take the form -xx value, with a
   space between the switch and the supplied value.  The yes-or-no
   settings get a value of "y" or "n".  However, starting with version
   2.6, XTide understands the following syntactic shortcuts:
     * Arguments can be concatenated with their switches.
     * A yes/no switch that omits its argument implies "y".
     * Using +xx instead of -xx for a yes/no switch inverts the argument
       (so if the argument is omitted, "n" is implied).

   Some shorthand forms are ambiguous.  For example, -lw5 could mean "set
   the line width to 5" (-lw 5) or it could mean "load the location named
   w5" (-l w5).  If this happens, you will get an error and will need to
   spell out what you meant.

   XTide*antialias
          Anti-alias tide graphs on true color displays? (y/n)
          Default: y
          Command line: -aa
          config.hh: antialias
          .xtide.xml: <xtideoptions aa="y"/>

   XTide*background
          Background color for text windows and location chooser.
          Default: white
          Command line: -bg
          config.hh: bgdefcolor
          .xtide.xml: <xtideoptions bg="white"/>

   XTide*buttoncolor
          Background color of buttons.
          Default: gray80
          Command line: -bc
          config.hh: buttondefcolor
          .xtide.xml: <xtideoptions bc="gray80"/>

   XTide*cbuttons
          Create tide clocks with buttons? (y/n)
          Default: n
          Command line: -cb
          config.hh: cbuttons
          .xtide.xml: <xtideoptions cb="n"/>

   XTide*cwidth
          Default width for tide clocks.  Note:  Default clock height is
          the same as default graph height (XTide*gheight).
          Default: 84
          Command line: -cw
          config.hh: defcwidth
          .xtide.xml: <xtideoptions cw="84"/>

   XTide*datefmt
          Strftime style format string for printing dates.
          Default: %Y-%m-%d
          Command line: -df
          config.hh: datefmt
          .xtide.xml: <xtideoptions df="%Y-%m-%d"/>

   XTide*datumcolor
          Color of datum line in tide graphs. [[6]*]
          Default: white
          Command line: -Dc
          config.hh: datumdefcolor
          .xtide.xml: <xtideoptions Dc="white"/>

   XTide*daycolor
          Daytime background color in tide graphs.
          Default: SkyBlue
          Command line: -dc
          config.hh: daydefcolor
          .xtide.xml: <xtideoptions dc="SkyBlue"/>

   XTide*ebbcolor
          Foreground in tide graphs during outgoing tide.
          Default: SeaGreen
          Command line: -ec
          config.hh: ebbdefcolor
          .xtide.xml: <xtideoptions ec="SeaGreen"/>

   XTide*eventmask
          Events to suppress (p = phase of moon, S = sunrise, s = sunset,
          M = moonrise, m = moonset), or x to suppress none.  E.g, to
          suppress all sun and moon events, set eventmask to the value
          pSsMm.
          Default: x
          Command line: -em
          config.hh: eventmask
          .xtide.xml: <xtideoptions em="x"/>

   XTide*extralines
          Draw datum and middle-level lines in tide graphs? (y/n) [[7]*]
          Default: n
          Command line: -el
          config.hh: extralines
          .xtide.xml: <xtideoptions el="n"/>

   XTide*flatearth
          Prefer flat map to round globe location chooser? (y/n)
          Default: n
          Command line: -fe
          config.hh: flatearth
          .xtide.xml: <xtideoptions fe="n"/>

   XTide*floodcolor
          Foreground in tide graphs during incoming tide.
          Default: Blue
          Command line: -fc
          config.hh: flooddefcolor
          .xtide.xml: <xtideoptions fc="Blue"/>

   XTide*font
          Font used for button labels and verbiage in text windows.
          Default: as incoming from X11
          Command line: -fn
          config.hh: N/A
          .xtide.xml: N/A

   XTide*foreground
          Color of text and other notations.
          Default: black
          Command line: -fg
          config.hh: fgdefcolor
          .xtide.xml: <xtideoptions fg="black"/>

   XTide*gaspect
          Default aspect for tide graphs.
          Default: 1.0
          Command line: -ga
          config.hh: defgaspect
          .xtide.xml: <xtideoptions ga="1.0"/>

   XTide*gheight
          Default height for tide graphs.
          Default: 312
          Command line: -gh
          config.hh: defgheight
          .xtide.xml: <xtideoptions gh="312"/>

   XTide*globelongitude
          Default center longitude for location chooser.
          Valid values: -180 -150 -120 -90 -60 -30 0 30 60 90 120 150 360
          360 will pick the longitude with the most tide stations.
          Default: 360
          Command line: -gl
          config.hh: defgl
          .xtide.xml: <xtideoptions gl="360"/>

   XTide*graphtenths
          Label tenths of units in tide graphs? (y/n)
          Default: n
          Command line: -gt
          config.hh: graphtenths
          .xtide.xml: <xtideoptions gt="n"/>

   XTide*gwidth
          Default width for tide graphs.
          Default: 960
          Command line: -gw
          config.hh: defgwidth
          .xtide.xml: <xtideoptions gw="960"/>

   XTide*hourfmt
          Strftime style format string for printing hour labels on time
          axis.
          Default: %l
          Command line: -hf
          config.hh: hourfmt
          .xtide.xml: <xtideoptions hf="%l"/>

   XTide*infer
          Use inferred values for some constituents.  For expert use only.
          Default: n
          Command line: -in
          config.hh: infer
          .xtide.xml: <xtideoptions in="n"/>

   XTide*lwidth
          Width for lines in tide graphs with nofill.
          Default: 2.5
          Command line: -lw
          config.hh: deflwidth
          .xtide.xml: <xtideoptions lw="2.5"/>

   XTide*markcolor
          Color of mark line in graphs and of location dots on the
          spinning globe.
          Default: red
          Command line: -mc
          config.hh: markdefcolor
          .xtide.xml: <xtideoptions mc="red"/>

   XTide*mslcolor
          Color of middle-level line in tide graphs. [[8]*]
          Default: yellow
          Command line: -Mc
          config.hh: msldefcolor
          .xtide.xml: <xtideoptions Mc="yellow"/>

   XTide*nightcolor
          Nighttime background color in tide graphs.
          Default: DeepSkyBlue
          Command line: -nc
          config.hh: nightdefcolor
          .xtide.xml: <xtideoptions nc="DeepSkyBlue"/>

   XTide*nofill
          Draw tide graphs as line graphs? (y/n)
          Default: n
          Command line: -nf
          config.hh: nofill
          .xtide.xml: <xtideoptions nf="n"/>

   XTide*nosunmoon
          Deprecated.  Use eventmask instead.
          Default: n
          Command line: -ns
          config.hh: N/A (use eventmask)
          .xtide.xml: <xtideoptions ns="n"/>

   XTide*pageheight
          Nominal length of paper in LaTeX output (mm). This need not
          match your actual paper; use "Shrink oversized pages" in print
          options.
          Default: 420
          Command line: -ph
          config.hh: defpageheight
          .xtide.xml: <xtideoptions ph="420"/>

   XTide*pagemargin
          Nominal width of top, bottom, left and right margins in LaTeX
          output (mm). Actual width will depend on print scaling.
          Default: 10
          Command line: -pm
          config.hh: defpagemargin
          .xtide.xml: <xtideoptions pm="10"/>

   XTide*pagewidth
          Nominal width of paper in LaTeX output (mm). This need not match
          your actual paper; use "Shrink oversized pages" in print
          options.
          Default: 297
          Command line: -pw
          config.hh: defpagewidth
          .xtide.xml: <xtideoptions pw="297"/>

   XTide*timefmt
          Strftime style format string for printing times.
          Default: %l:%M %p %Z
          Command line: -tf
          config.hh: timefmt
          .xtide.xml: <xtideoptions tf="%l:%M %p %Z"/>

   XTide*toplines
          Draw depth lines on top of tide graph? (y/n)
          Default: n
          Command line: -tl
          config.hh: toplines
          .xtide.xml: <xtideoptions tl="n"/>

   XTide*ttyheight
          Height of ASCII graphs (characters).
          Default: 24
          Command line: -th
          config.hh: defttyheight
          .xtide.xml: <xtideoptions th="24"/>

   XTide*ttywidth
          Width of ASCII graphs, banners, and calendars (characters).
          Default: 79
          Command line: -tw
          config.hh: defttywidth
          .xtide.xml: <xtideoptions tw="79"/>

   XTide*units
          Preferred units of length: ft, m, or x (no preference).
          Default: x
          Command line: -u
          config.hh: prefunits
          .xtide.xml: <xtideoptions u="x"/>

   XTide*zulu
          Coerce all time zones to UTC? (y/n)
          Default: n
          Command line: -z
          config.hh: forceZuluTime (XTide 2.9+) or zulu (previously)
          .xtide.xml: <xtideoptions z="n"/>

   [*] The National Ocean Service (NOS) defines both Mean Sea Level (MSL)
   and Mean Tide Level (MTL) in terms of averages taken over
   observations.  The middle-level line is drawn at the midpoint of the
   theoretical tidal range, which usually corresponds to the mathematical
   mean level of the predictions.  This approximates both MSL and MTL,
   but, strictly speaking, is equivalent to neither.  Moreover,
   subordinate station offsets may shift the actual mean so that it no
   longer falls at the midpoint of the tidal range.  The datum line is
   drawn at the zero level of the predictions, which usually corresponds
   to the station's benchmark, but this too can be rendered inaccurate by
   subordinate station offsets.

Format of ~/.xtide.xml

   If you have compiled the interactive client (xtide), then you do not
   need to worry about ~/.xtide.xml at all, because the control panel will
   configure it for you automatically.

   In the event that you cannot use xtide but still need to make some
   settings for the command line client, use the example below as the
   starting point for your ~/.xtide.xml file.  This example just sets the
   TTY geometry.  You can add more settings by adding more attributes
   (like the tw and th attributes shown here) to the xtideoptions entity.
   The attributes that are recognized for each setting are documented
   above.

<?xml version="1.0"?>
<xtideoptions tw="79" th="24"/>
     __________________________________________________________________

   [9]<- Previous [10]-> Next [11]Contents

References

   1. http://www.flaterco.com/xtide/xttpd.html
   2. http://www.flaterco.com/xtide/harmonics.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/advanced.html#cp
   6. http://www.flaterco.com/xtide/settings.html#splat
   7. http://www.flaterco.com/xtide/settings.html#splat
   8. http://www.flaterco.com/xtide/settings.html#splat
   9. http://www.flaterco.com/xtide/xttpd.html
  10. http://www.flaterco.com/xtide/harmonics.html
  11. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Portland Head Light

About harmonic constants and sub station corrections
(What to do if your location isn't listed)

   As was explained in the [5]introduction, tide predictions for a given
   location cannot be conjured out of the void--you need to get some
   special data for each and every location for which you want to predict
   tides.  XTide reads these data from harmonics files.  Information on
   obtaining harmonics files is at
   [6]http://www.flaterco.com/xtide/files.html#harmonicsfiles.

   Currently there are two sources of harmonics files.  David Flater
   maintains a conservative set of data, emphasizing responsiveness to
   updates and traceability to authoritative sources instead of maximum
   coverage of locations and historical predictions.  These data and the
   list of locations they support can be found at
   [7]http://www.flaterco.com/xtide/files.html#harmonicsfiles.  Bob Kenney
   maintains a more liberal set of data, retaining some data that are old
   and expired in order to support users who continue to get good results
   with the old data.  These data and the much longer list of locations
   they support can be found at
   [8]http://harmonics.unh.edu/xtide/files.html.  Because they are out of
   date, use of these legacy data is not recommended.

   Check to make sure that your location does not appear anywhere in these
   harmonics files by any alias.  If your location is not already on the
   list, you need to obtain either a set of harmonic constants or a set of
   corrections and send this information to David Flater and/or Bob
   Kenney, as appropriate.  You could import these data yourself using the
   tools available at [9]http://www.flaterco.com/xtide/files.html, but
   please forward the data anyway so that others may benefit.

  Harmonic constants

   [10]National Ocean Service tide station at Bar Harbor, Maine

   Harmonic constants of the first kind, the kind worth having, are
   created by analysis of regular water level readings taken by automated
   tide stations like the one pictured here.  Harmonic constants of the
   second kind, the kind not worth having, are created by mangling the
   first kind to approximate the results of applying corrections.  We are
   only interested in the first kind.  XTide can do corrections properly,
   so mangled data just junk up the database.

   [11]harmonics-dwf contains all U.S. stations available from the NOS web
   site.  If it has fallen out of date, email [12]dave@flaterco.com to
   check whether an update is in progress.

   In countries other than the U.S., you might have a really hard time
   getting the resident tide-predicting authority to release harmonic
   constants.  They may be paternalistic, not wanting to trust
   non-government people with something as dangerous as tide prediction.
   They may be fearful that the data will be used to time an invasion by
   sea.  Or they may simply want to retain a monopoly on tide predictions,
   for whatever rea$on.  Regardless, if you do manage to obtain harmonic
   constants, please obtain and forward a statement from the authority
   either granting permission for non-commercial use or explaining that
   such permission is not required.

   There is a collection of old harmonic constants for ports world wide
   that had to be withdrawn because of the permissions issue (for the full
   sob story, see the [13]FAQ).  If you have contact with your local
   marine authorities and could obtain and forward a statement that use of
   these tide data is not restricted in your region, Mr. Kenney could
   reinstate the old data.  However, it would be better if they just sent
   us the newest data.

   If you have access to at least a year's worth of regular water level
   readings for some locale, you can derive the harmonic constants
   yourself using the Harmgen program available from
   [14]http://www.flaterco.com/xtide/files.html#experts, or send the time
   series to [15]dave@flaterco.com (again, with all necessary permissions
   attached) and harmonic constants will be derived for you, time
   permitting.

  Corrections

   A subordinate station is a tide station whose predictions are obtained
   by applying corrections to a reference station, i.e., one for which we
   have good harmonic constants.  The words 'corrections,' 'differences,'
   and 'offsets' are used interchangeably.

   [16]harmonics-dwf contains all U.S. stations available from the NOS web
   site.  If it has fallen out of date, email [17]dave@flaterco.com to
   check whether an update is in progress.

   While harmonic constants can be hard to get, you should be able to get
   offsets with relative ease from a local boating magazine, chartbook,
   yacht club, or marine authority.  If you find suitable offsets, you can
   add them to harmonics.tcd using the tideEditor program available from
   [18]http://www.flaterco.com/xtide/files.html#extras.  There are two
   other ways to do it (via build_tide_db in tcd-utils or via Harmbase 2),
   but tideEditor is most expedient for the non-expert.

    General notes and warnings

     * There are many different flavors of offsets for subordinate
       stations.  At this time, XTide supports all commonly appearing
       flavors except for the Admiralty one that has different height
       differences depending on the time of month.  The following rare and
       freakish sorts are not supported:  those that use different offsets
       depending on whether the flood at the reference station crossed
       some threshold; those that rely on more than one reference station;
       those that use different offsets for higher high or low water
       versus lower high or low water; currents that use a regular tide
       station as reference, or vice-versa.
     * If you can't find the latitude and longitude, just estimate the
       coordinates as best you can using an atlas.
     * The timezone attribute is only used to choose the time zone in
       which to render output for the location.  In the majority of cases
       this will be the same as for the reference station.  However, if
       your reference station is in a different time zone, you may need to
       alter the time offsets to REMOVE compensation for the time zone
       difference.  In XTide, offsets are independent of the time zone.
     * If you don't get slack offsets (floodbegins, ebbbegins) for a
       current station, OMIT those fields!  When slack offsets are
       omitted, XTide will interpolate a reasonable value.  But if you
       specify zero, you get zero--even if that's unreasonable with
       respect to the specified max and min.

    Adding corrections using tideEditor 1.4

   First make a backup copy of whatever you are about to modify.

   TideEditor version 1.4 takes the name of the file to modify as the
   command-line argument.

bash-3.1$ tideEditor whatever.tcd

   When you start tideEditor, you get a map of the world.  Point at the
   location where you want to add a subordinate station and right click.

   You will get a prompt asking "Will the new station be a reference
   station or a subordinate station?"  Choose Subordinate.

   You will get a prompt saying "Please select the new reference
   station."  Use the pull-down list to select the reference station and
   click OK.

   You will then get a window with the tabs General, Verbiage and Offsets,
   initially showing General.  On the General tab, the Reference Station,
   Latitude and Longitude fields will be pre-filled based on your previous
   actions.  The other fields that you MUST fill in are as follows:
     * Station Name:  Enter the name of the new subordinate station.
     * Time Zone:  Use the pull-down to set the time zone (select the
       major city for the applicable region).
     * Level Units:  Select feet or meters for tides, knots for currents.

   All other fields on the General and Verbiage tabs are optional.
   Descriptions of the other fields are obtainable using the question mark
   tool thingy ( [whatsthis.png] ).

   The Offsets tab has the following fields.
     * Minimum Time Add.  The time adjustment for low tide / max ebb.  It
       is expressed as an integer that is hours times 100 plus minutes, so
       for -0:20 (negative 0 hours, 20 minutes) you would write -20, and
       for 1:40 (positive 1 hour, 40 minutes) you would write 140.  If you
       don't have this, leave it blank.
     * Minimum Level Add.  A value, in the units identified by Level
       Units, that is added to the tide level or current velocity
       predicted at low tide or max ebb.  If you don't have this, leave it
       blank.
     * Minimum Level Multiply.  A multiplier for the tide level or current
       velocity predicted at low tide or max ebb.  If you don't have this,
       leave it blank.
     * Maximum Time Add, Level Add, and Level Multiply are analogous, but
       correspond to high tide / max flood.
     * Flood Begins.  Another kind of "Time Add" used only by currents to
       adjust the time of the slack preceding a flood.  If you don't have
       this, leave it blank.  If it got initialized to zero, make it
       blank.
     * Ebb Begins.  Analogous to Flood Begins.

   When finished, click OK.  When you quit tideEditor, your new station
   will be saved in the updated TCD file.

   Notations used to describe corrections will vary:

    Notation              Translation
   -0:20       Time Add -20
   1 23        Time Add 123
   *1.07       Level Multiply 1.07
   +0.4        Level Add 0.4
   (*0.65+0.3) Level Multiply 0.65, Level Add 0.3

   If you were not given separate corrections for max and min, set both
   the max and min values to whatever you got.  For example, if you get

Head Harbor, Isle au Haut    -0:20   (Portland)

   then you should set both Minimum Tide Add and Maximum Time Add to -20.
     __________________________________________________________________

   [19]<- Previous [20]-> Next [21]Contents

References

   1. http://www.flaterco.com/xtide/settings.html
   2. http://www.flaterco.com/xtide/bugs.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/introduction.html
   6. http://www.flaterco.com/xtide/files.html#harmonicsfiles
   7. http://www.flaterco.com/xtide/files.html#harmonicsfiles
   8. http://harmonics.unh.edu/xtide/files.html
   9. http://www.flaterco.com/xtide/files.html
  10. http://www.flaterco.com/
  11. http://www.flaterco.com/xtide/files.html#harmonicsfiles
  12. mailto:dave@flaterco.com
  13. http://www.flaterco.com/xtide/faq.html#60
  14. http://www.flaterco.com/xtide/files.html#experts
  15. mailto:dave@flaterco.com
  16. http://www.flaterco.com/xtide/files.html#harmonicsfiles
  17. mailto:dave@flaterco.com
  18. http://www.flaterco.com/xtide/files.html#extras
  19. http://www.flaterco.com/xtide/settings.html
  20. http://www.flaterco.com/xtide/bugs.html
  21. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Lobster boat and the big ocean, Ogunquit, Maine, 1998-06-08.

Quirks to be aware of

    1. Graphs actually begin a little bit earlier than the nominal start
       time so that the specified start will appear immediately to the
       right of the labels for the depth axis instead of being obscured by
       them.
    2. The effective end time for graph mode is entirely determined by the
       start time, the graph width, and the aspect.  If an end time is
       also specified by the user, it is ignored.
    3. XTide uses shorter descriptions for the tide events listed across
       the bottom caption line in tide graphs whenever the descriptions
       get to be longer than the timestamps.  Consequently, changing the
       time format setting to something more concise causes the
       descriptions to get shorter too, which is what you want.  However,
       this behavior can result in cosmetic inconsistencies; e.g., with
       default settings, "Mark Rising" is matched by "Mark" instead of
       "Mark Falling," because the one additional letter puts it over.
    4. The -o command line switch causes output to be appended to the
       specified file instead of overwriting it as is the generally
       accepted custom.
    5. While XTide-specific command-line arguments can be concatenated
       with their switches or not, the arguments to standard X11 switches
       sometimes must be separate to work.  Affected switches include
       -display, -fn, and -geometry.
    6. What XTide does about minimum current events at subordinate
       stations might not be what you expect.  See [5]Appendix B for
       details.

Known limitations

    1. RGB color specs (rgb:N/N/N) in sizes other than 24 bits
       (rgb:hh/hh/hh) generally will not work.
    2. All timestamps have a precision of plus or minus one minute.
    3. All predictions are made to an accuracy of plus or minus one minute
       (in the mathematical sense, not in the sense of matching up with
       the real world).
    4. URLs assigned to specific locations by the xttpd web server are
       rather transient and will change whenever the harmonics files are
       updated.  The xttpd web space will remain internally consistent,
       but hyperlinks from outside pages will be screwed.
    5. Moonrise and moonset don't work before 1900 or after 2099.
    6. The time scale for stations claiming to be in UTC is not strictly
       speaking UTC since it does not implement [6]leap seconds.  The
       maximum discrepancy as of 2007 is 23 seconds, which is still "below
       the noise."
    7. If a subordinate station has absurd offsets that cause low tides to
       become higher than high tides, the mathematical upper and lower
       bounds reported by stats mode may be incorrect.
    8. When specifying location names on the command line, multiple data
       sets having the same name cannot be distinguished, and it is not
       deterministic which one you will get.
    9. XTide is untested and probably dysfunctional on any platform where
       time_t is a non-integral type.  It would probably still work with
       --enable-time-workaround.
   10. XTide assumes that the first 256 characters of the default X11 font
       agree with ISO-8859-1.

Known bugs

    1. If the control panel is resized, dismissed, and then shown again,
       its buttons are missing.  Cause of bug:  Don't know.  Workaround:
       Close the control panel using the window manager (e.g., hit the 
       in the upper right corner) and then show it again.  The control
       panel retains its new size but the buttons reappear.
    2. Some of the dialog windows cause harmless but annoying toolkit
       warnings when you dismiss them.  Cause of bug:  Don't understand
       what the toolkit grabs are doing.  Workaround:  Ignore warnings.
    3. Line width in line graphs isn't maintained when the slope of the
       graph becomes drastic.  Cause of bug:  Need better algorithm for
       drawing line graphs.  Workaround:  Set the aspect higher.
    4. Buttons will sometimes shift out from under the mouse pointer and
       get "stuck on."  Cause of bug:  (1) button moves due to changing
       geometry of other things in the box, leading to (2) button shifts
       out from under the pointer, which triggers (3) bug in Athena
       Widgets where the button release event gets lost.  Workaround:  As
       needed, click on the stuck button to un-stick it.  This problem can
       be prevented in the control panel by specifying a fixed-width font
       with the -fn switch, which avoids (1).  The bug is less likely in
       other windows.
    5. The analog tide clock icon flashes when it updates, and doesn't
       update at all under some window managers.  Alternate symptom:  Tide
       clocks crash the window manager at random.  Cause of bug:  Window
       managers don't expect icons to keep changing and aren't designed to
       handle it properly.  Workaround:  Use a window manager that doesn't
       suck.
    6. Dialog boxes don't behave like you would expect when you hit the
       Enter key.  Cause of bug:  Athena widgets use multi-line buffers
       even for one-line fields.  Workaround:  Don't hit Enter.
    7. Syslog messages generated by xttpd have timestamps in UTC or random
       time zones intead of local time, which is highly confusing in a log
       that is otherwise in local time.  Cause of bug:  Design defect of
       syslog():  Every program logs in whatever time zone it happens to
       be using at the time instead of a standard zone.  XTide needs to
       adopt the time zone of each station to generate predictions for
       it.  Workaround:  none.
     __________________________________________________________________

   [7]<- Previous [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/harmonics.html
   2. http://www.flaterco.com/xtide/faq.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/mincurrents.html
   6. http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm
   7. http://www.flaterco.com/xtide/harmonics.html
   8. http://www.flaterco.com/xtide/faq.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Perkins Cove, Maine, 1998-06-09

Frequently Asked Questions

   Note:  "Mumble Foo Bar" is a made-up place that is meant to represent
   whatever place you are looking for.  Whatever is said in this FAQ about
   Mumble Foo Bar applies to your location as well.

  FAQ of the Day

     * [5]Are these predictions compliant with the new 2007 Daylight
       Savings Time rules for the U.S.?

  Ultra-high frequency questions

     * [6]Your WWW Tide and Current Predictor blah blah blah...
     * [7]Can you send me predictions for Mumble Foo Bar?
     * [8]URGENT - DROP EVERYTHING AND READ THIS!  The race starts in 5
       hours so I need a tide chart for Mumble Foo Bar NOW!
     * [9]Can you tell me where I can find a web page with predictions for
       Mumble Foo Bar?
     * [10]Can you please add predictions for Mumble Foo Bar?
     * [11]How do I make the calendar print all on one page?
     * [12]Can you tell me the offsets for Mumble Foo Bar?
     * [13]There are multiple listings for the same place, and they give
       different results.  What's going on?
     * [14]Can you predict the tide and/or current if I give you the
       latitude and longitude?
     * [15]The coordinates you provide for Mumble Foo Bar are off by
       miles.
     * [16]Why are there no currents in the latest database?

  XTide operational questions

     * [17]I am doing some historical research and need to project what
       the tides would have been a long long time ago.
     * [18]I live outside of the U.S. and my location is no longer
       supported.  What happened?
     * [19]The predictions for somewhere in the U.S.A., Mexico or Nunavut
       are off by one hour or six hours.
     * [20]For Chesapeake and Delaware Canal Current, Flood and Ebb are
       not informative.  Which way is which?
     * [21]For Cape Cod Canal Current, Flood and Ebb are not informative.
       Which way is which?
     * [22]When compiling XTide, I get errors like....
     * [23]I want to change the end time of a tide graph but the settings
       that I make have no effect.
     * [24]The text in XTide windows is formatted ugly.
     * [25]When I run xttpd, it exits immediately with no errors to tell
       me what went wrong.
     * [26]I always get a warning about "using obsolete time zone
       database."
     * [27]How do I switch from tide to current predictions or vice-versa
       for a given location?
     * [28]What are bogo-knots?
     * [29]First it says high tide is at 3:15 PM but then when I run it
       again it says 3:14 PM.
     * [30]Has this been ported to Windows / PalmOS / anything but Unix?
     * [31]Xttpd sucks!  Can't XTide work with PHP?
     * [32]The tides for my location are totally wrong!
     * [33]The tides for Mumble Foo Bar are obviously bogus because they
       have too many high tides on this day / only one high tide on this
       day / tides that are just a few minutes apart.
     * [34]I have five constituents and some seasonal corrections for my
       location.  Can you get this to work?

  General tide related questions

     * [35]I have a tide watch that only goes through the year 1999.  What
       year could I set it to that would be the same as this year?
     * [36]Is there a set time advancement each day for the next high and
       low tide?  Does it always repeat 12 1/2 hours later?
     * [37]Somebody gave me a tide clock, but the instructions say it only
       works on the east coast.  How can this be?
     * [38]Why do the high and low tides have such different levels to
       them on any given day?
     * [39]If it's high tide here, is it low tide in [faraway place]?
     * [40]What does the zero (0) on a tide chart represent?
     * [41]Why is it that the tides two miles from here are an hour
       different than the tides here?
     * [42]Why are there two high tides per day, anyway?  How is this
       possible?
     * [43]What does "slack water" mean?
     * [44]I have a theory that [random phenomenon] is related to tidal
       forces, but I am landlocked.  Can you, like, predict the "tides"
       for [landlocked location]?
     * [45]I want to write my own tide predicting program.  Can you
       provide a SIMPLE explanation of the tide-predicting function?

  Business questions

     * [46]I want to license XTide so I can build a commercial product
       around it.
     * [47]I have a lot of specific questions about the GNU General Public
       License and/or want a ruling that my specific plan is OK.
     * [48]We are a non-profit and we want to sell calendars with
       predictions from your web site.  Is that OK?
     * [49]I have a great idea to make money selling tide predictions, but
       I'm not good with technical stuff, so would you just do this for
       me...
     * [50]I already make money selling tide prediction products, but your
       stuff is better, so would you just do this for me...
     * [51]I need to do [poorly researched brainstorm having something to
       do with tide prediction]--how much would you charge in consulting
       fees to help me do it?

  Academic questions

     * [52]How should I cite XTide within publications?

  Questions that you should have asked, but didn't

     * [53]What is the difference between a reference station and a
       subordinate station?
     * [54]These predictions are nonsense--what is going on here?
     * [55]Where can I find tons of information about tides that is both
       more authoritative and better written than this FAQ?
     __________________________________________________________________

  FAQ of the Day

   Q: Are these predictions compliant with the new 2007 Daylight Savings
   Time rules for the U.S.?

   A: XTide relies on [56]the de facto standard time zone database to
   handle Daylight Savings Time.  XTide's results will obey the new
   Daylight Savings Time rules if and only if the version of zoneinfo
   installed is sufficiently new.  See [57]System Requirements.

  Ultra-high frequency questions

   Q: Your WWW Tide and Current Predictor blah blah blah...

   A: I am not the maintainer of the [58]WWW Tide and Current Predictor.
   I am the maintainer of [59]XTide.  Although the [60]WWW Tide and
   Current Predictor uses some version of [61]XTide behind the scenes, I
   have no control over the behavior of the web site or its maintenance.

   Q: Can you send me predictions for Mumble Foo Bar?

   A: I cannot possibly provide this level of service to everyone who
   wants it.  Please use a commercial service and/or a web site.

   Q: URGENT - DROP EVERYTHING AND READ THIS!  The race starts in 5 hours
   so I need a tide chart for Mumble Foo Bar NOW!

   A: You might not believe it, but sometimes I go two weeks without
   reading my e-mail.  Really!  And when I do get back to it, there are
   always lots of messages just like this one, so far past their use-by
   dates that green fuzz has started to grow on them.  The answer is the
   same:  I cannot possibly provide this level of service to everyone who
   wants it.  Please use a commercial service and/or a web site.

   Q: Can you tell me where I can find a web page with predictions for
   Mumble Foo Bar?

   A:
     * Germany:  [62]Bundesamt fr Seeschifffahrt und Hydrographie (BSH)
     * Netherlands:  [63]Ministerie van Verkeer en Waterstaat
     * New Zealand:  [64]Land Information New Zealand (LINZ)
     * Norway:  [65]Norwegian Hydrographic Service
     * U.K.:  [66]National Tidal and Sea Level Facility (NTSLF)
     * U.K.:  [67]U.K. Hydrographic Office
     * U.S.A.:  [68]National Ocean Service (NOS), Center for Operational
       Products and Services (CO-OPS)

   Q: Can you please add predictions for Mumble Foo Bar?

   A: Probably not.  Please read the section entitled [69]What to do if
   your location isn't listed.

   Q: How do I make the calendar print all on one page?

   A: The short answer for Windows XP users is to do the following:
    1. Bring the calendar up in Internet Explorer version 7 (not 6).
    2. Click the arrow to the right of the Print button, and then click
       Print Preview.
    3. Pull down the print size menu ( Shrink To Fit ) and try different
       options until the calendar fits nicely on a page.
    4. When ready, click on the tiny printer icon to print.

   For a more complete answer and/or instructions tailored for Linux, see
   [70]Appendix C.

   Q: Can you tell me the offsets for Mumble Foo Bar?

   A: You can get them easier than I can by checking the sources described
   in the section entitled [71]What to do if your location isn't listed.

   Q: There are multiple listings for the same place, and they give
   different results.  What's going on?

   A: There are two different approaches to predicting the tides at a
   given place.  One approach is to calculate them directly from a data
   set; when this is done it is called a "reference station."  The other
   approach is to estimate them using adjustments to the tides at a nearby
   reference station; when this is done it is called a "subordinate
   station."

   Data gathered from the NOAA web site sometimes include both a reference
   station and a subordinate station for the same place.  For example, the
   subordinate station may be used for published tide tables while the
   reference station is still relatively new and untested.  The results
   will differ, but they should be close (assuming that there are no
   problems with the data).  If you are concerned about matching
   predictions up with those from some particular source, you should try
   each data set and see which one matches the best.

   In rare cases, data gathered from the NOAA web site include two
   reference stations or two subordinate stations with exactly the same
   name and nearly the same location.  When this happens, one of them has
   (2) suffixed to its name.  Again, if you are trying to match official
   predictions, you should try both to determine which is better.

   If you are using old legacy data or a web site that does, you may see
   additional listings for the same place.  These may be expired and/or
   have dubious traceability to authoritative sources.  They cannot be
   expected to agree with up-to-date predictions.

   Q: Can you predict the tide and/or current if I give you the latitude
   and longitude?

   A: The short answer is no.  XTide cannot predict tides unless you
   provide harmonic constants (see [72]What to do if your location isn't
   listed).

   From what I'm told, the tide models that were built from
   [73]TOPEX/Poseidon data work on a global scale, but they are inaccurate
   on continental shelves.  Some organizations have constructed models
   that function in coastal waters in localized regions.  For example,
   NIWA has a [74]model for New Zealand's coastal waters, and NOAA has a
   [75]model of currents in San Francisco Bay.  Although XTide could make
   use of harmonic constants generated from these models, XTide does not
   implement any such models.

   Q: The coordinates you provide for Mumble Foo Bar are off by miles.

   A: XTide reports coordinates in degrees only.  Some sources report
   coordinates in degrees and minutes and run these together in a
   confusing way.  For example, a coordinate shown as 2846.330 may
   actually mean 28 degrees, 46.330 minutes, which XTide would report as
   28.7722 degrees.  If this is not sufficient to explain the discrepancy
   then by all means report the problem.  All coordinates in the latest
   harmonics data are traceable to an authoritative source.

   Q: Why are there no currents in the latest database?

   A: The [76]Center for Operational Oceanographic Products and Services
   (CO-OPS) of [77]NOAA's [78]National Ocean Service (NOS) does not
   presently supply harmonic constants for currents on its public web
   site.  This text from [79]http://tidesandcurrents.noaa.gov/ncop.html
   may partially explain why not:

     Approximately 70 percent of the stations in the 2001 Tidal Current
     Tables are over 30 years old.  Many of these stations are based on
     analyses of less than 7 days of data (the data duration is known for
     24% of all stations).  Channel dredging and changes in the
     configuration of ports and harbors over the years have significantly
     altered the physical oceanography of many of the nation's
     estuaries.  Reports from local users indicate that many of NOS's
     tidal current predictions may be inaccurate.  NOS intends to address
     these deficiencies by rebuilding the program and resampling the
     currents at every major port and estuary within the next 20 years.

  XTide operational questions

   Q: I am doing some historical research and need to project what the
   tides at Mumble Foo Bar would have been a long long time ago.

   A: This is generally ill-advised.

   It is technically possible to get XTide to make projections back to 1
   AD (see [80]Appendix A for details).  However, such projections are
   usually unverifiable and are likely to be wildly inaccurate.  If you
   work from these projections with no means of independent verification,
   you deserve what you get.

   The perishability of tide data for a given location varies depending on
   how quickly the local topography changes.  Some places go rotten in
   less than a decade.  All locations are impacted by global sea level
   change, which becomes significant in less than a century.

   Over even longer spans, the physics start to go wrong.  Some of the
   astronomical "constants" used in the U.S. method of tide prediction
   really aren't constant; they change very slowly.  For example, the
   speeds of harmonic constituents change.  We are still using constant
   speeds that were calibrated for the year 1900.  When you change the
   speeds of the harmonic constituents, it changes everything.  As we get
   too far away from 1900 in either direction, eventually the model
   collapses and the results are garbage.  As far as I know, nobody has
   done an analysis to determine exactly when this occurs.

   When this happens in the future, we can just update the speeds and
   generate fresh harmonic constants that work within the new model.  But
   we can't do that for historical predictions because we don't have the
   water level observations from that period in history to derive the
   harmonic constants.  We have no choice but to use the physics of 1900,
   with data derived from observations in 2000, to extrapolate back to
   whenever, and hope that we haven't pushed the model too far.

   Needless to say, the credibility of projections for anywhere reaches
   zero well before you get back to 1 AD.  So please don't ask for BC
   support.

   Q: I live outside of the U.S. and my location is no longer supported.
   What happened?

   A: After a legal threat from the U.K. Hydrographic Office (UKHO) and
   the subsequent discovery that country-by-country permissions are now
   required to use harmonic constants (the data needed to predict tides),
   all of the data that arrived via the International Hydrographic Office
   (IHO) or the Table des Mares des Grands Ports du Monde (TMGPM) were
   removed from the harmonics files in January 2001.

   Back in the old days, the collection of hydrographic data was done
   almost exclusively using public funds.  The resulting harmonic
   constants were treated as scientific results, published, and
   distributed on request from an international data bank.  But in the
   late 20th century, a wave of privatizations occurred, and harmonic
   constants became the intellectual property of the collecting agencies.

   You wouldn't think it possible to "un-publish" data that were
   distributed with considerable freedom at one time.  Nevertheless, the
   international data bank was abolished, the Table des Mares des Grands
   Ports du Monde was withdrawn from publication, and I was coerced into
   removing the associated data from the harmonics files.

   Was I spineless?  Perhaps.  Those who wrote the threatening letter
   clearly had not done their homework and may have overreached their
   jurisdiction.  But even with the benefit of hindsight and experience,
   knowing that some unethical companies habitually make legal threats to
   manipulate people into doing things that they aren't necessarily
   obliged to do, I don't blame myself for not fighting it.  Why take a
   risk for the sake of some tide data of questionable pedigree that were
   doomed to become useless from age pretty soon anyway?

   For my own part, I do not consider privatization to be inherently
   evil.  It would have been reasonable to keep newly generated data
   secret while leaving the old data in the public domain until their
   useful life expired.  But in my opinion it was wrong to lay claim to
   the old data that were once shared in the spirit of scientific
   openness.  It was a disservice and dishonor to all of us who accepted
   those data on good faith and donated our own time to maintain them and
   add value to them to end up accused of copyright infringement.  For
   someone who had invested himself in writing free software as a public
   service, the reward was a slap in the face.

   Although only the UKHO made an issue of it, the fact that they did
   sufficed to "poison" all of the IHO and TMGPM data for every country.
   We can no longer assume that we have permission to use any of them.  In
   countries other than the U.K., if you have contact with your local
   marine authorities and could obtain and forward to Mr. Kenney a
   statement that use of the old data is not restricted in your region,
   they could be reinstated.  (Bob Kenney is the maintainer of a database
   of legacy data that can be used by XTide and other programs.  You can
   find it on his web site at
   [81]http://harmonics.unh.edu/xtide/files.html.)  However, if they have
   newer data, it would be better if they just sent those to me and Mr.
   Kenney with all necessary permissions attached.  I regret that former
   British colonies having no independent tide authority have effectively
   been disenfranchised.

   In 2003-12, new data for 44 stations in the U.K. became available
   thanks to the generosity of the [82]British Oceanographic Data Centre
   (BODC) based at the [83]Proudman Oceanographic Laboratory in
   Liverpool.  The legal details can be found at
   [84]http://flaterco.com/pol.html.  I encourage other organizations who
   maintain tide gauges anywhere in the world to contact us about deriving
   some harmonic constants.

   Q: The predictions for somewhere in the U.S.A., Mexico or Nunavut are
   off by one hour or six hours.

   A: The referenced nations have recently made changes to their time
   zones or daylight savings time rules.  In order for XTide to give
   predictions in local time correctly, a recent version of the Zoneinfo
   library must be installed.  You can obtain this library from
   [85]ftp://elsie.nci.nih.gov/pub/.

   Q: For Chesapeake and Delaware Canal Current, Flood and Ebb are not
   informative.  Which way is which?

   A: Based on observations by Richard W. Reynolds and friends, it appears
   that "Flood" for this data set indicates that water is flowing from the
   Chesapeake to the Delaware bay.

   Q: For Cape Cod Canal Current, Flood and Ebb are not informative.
   Which way is which?

   A: According to Reinhard Schumann, "Flood" for this data set means
   "current towards the east."  Woods Hole current is probably the same.

   Q: When compiling XTide, I get errors like....

   A: Please refer to the [86]troubleshooting section of the installation
   instructions.  If your error is not shown there, please email
   [87]dave@flaterco.com for assistance.

   Q: I want to change the end time of a tide graph but the settings that
   I make have no effect.

   A: This is [88]Quirk #2.  In graph mode, the end time is determined by
   the applicable width and aspect, not the other way around.  Thus,
   neither the -e switch nor the compiled-in defpredictinterval constant
   have any effect in this case.  In the interactive client, you can
   resize the window as you would any window and change the aspect from
   the Options menu.  The applicable command-line switches are -gw for
   X-windows or PNG formats, -tw for text format, and -ga.  For more
   details, refer to "[89]Customizing XTide."

   Q: The text in XTide windows is formatted ugly.

   A: For windows containing lots of text, XTide uses the default font
   offered by the X11 environment.  If this is not a monospace font, the
   results could indeed be ugly.  The default font can be overridden using
   the command line switch -fn.  Give this a try:

     xtide -fn "-adobe-courier-bold-r-normal-*-12-*-*-*-*-*-iso8859-1"

   If that looks better, you can make the change permanent by adding this
   line to your ~/.Xresources file:

     XTide*font: -adobe-courier-bold-r-normal-*-12-*-*-*-*-*-iso8859-1

   Q: When I run xttpd, it exits immediately with no errors to tell me
   what went wrong.

   A: When executed, xttpd immediately dissociates from your terminal and
   starts logging all diagnostics to syslog.  So look in your system
   logs.  You will find these someplace like /var/log or /var/adm/log.

   Q: I always get a warning about "using obsolete time zone database."

   A: Please see the [90]System requirements section for details of what
   this means and what you can do to fix it.

   Q: How do I switch from tide to current predictions or vice-versa for a
   given location?

   A: Alas, although the two are clearly connected in the physical world,
   they are unrelated from the perspective of XTide.  Even for the same
   location, tide predictions and current predictions require two
   completely separate data sets, and rarely will you get both.  As of
   2005-01, there are no currents available in the latest data (the
   National Ocean Service has not made them available on their web site).
   If current predictions are available for a location in legacy data,
   they will appear in the location list with the word "Current" at the
   end of the name.

   Q: What are bogo-knots?

   A: If you are still seeing bogo-knots, then you are definitely using
   obsolete data and an obsolete version of XTide, or accessing a web site
   that is using obsolete data and an obsolete version of XTide.  I am not
   the maintainer of any such web sites, and I recommend upgrading to
   XTide 2, which will barf all over any harmonics files that still
   contain "bogo-knots."

   Q: First it says high tide is at 3:15 PM but then when I run it again
   it says 3:14 PM.

   A: XTide's accuracy is plus or minus one minute.  The behavior that you
   witnessed is normal.

   Q: Has this been ported to Windows / PalmOS / anything but Unix?

   A: Yes, to varying degrees.  Please see the [91]ports page.

   Q: Xttpd sucks!  Can't XTide work with PHP?

   A: A number of people have expressed interest in getting XTide to work
   through PHP.  Thus far I have just been introducing them to each other
   through e-mail and waiting for cool things to happen.  There is now a
   [92]WordPress plugin by Mir Rodrguez.

   Q: The tides for my location are totally wrong!

   A: Unfortunately, there have been some problems recently with data sets
   being assigned the wrong meridians upstream.  The symptom is that all
   predictions are shifted earlier or later by the same number of hours.
   If you can verify that this has happened by comparison with published
   tide tables (available at
   [93]http://tidesandcurrents.noaa.gov/tides07/), please report the
   problem for corrective action.

   Q: The tides for Mumble Foo Bar are obviously bogus because they have
   too many high tides on this day / only one high tide on this day /
   tides that are just a few minutes apart.

   A: That is not necessarily a problem.  Some places really do have only
   one tide cycle per day.  Others generate "extra" tides when the tidal
   forces align in such a way as to produce a "double" high or low tide or
   a temporary reversal near mid-tide.  These extra tides can be
   arbitrarily close together.  Official predictions might omit them, but
   XTide faithfully reports all maxima and minima that it finds.

   The legacy data contain some data sets in which harmonic constants were
   generated for subordinate stations by munging the constants of a
   reference station.  This operation was fragile and sometimes it led to
   spurious maxima and minima.  The fix is to upgrade to the latest data,
   which contains no "munged" data sets.

   Q: I have five constituents and some seasonal corrections for my
   location.  Can you get this to work?

   A: XTide is not presently enabled to handle seasonal corrections
   directly.  To my knowledge, seasonal corrections are only used in
   publications by the British Admiralty that do not allow redistribution
   of data, so the value of providing better support for them in XTide
   would be marginal at best.  However, if you have legal access to such
   data and are determined to use it with XTide, it may be possible to
   synthesize values for long-term constituents to "approximate the
   approximation."  A spreadsheet for doing this is available from
   [94]http://www.flaterco.com/xtide/files.html#experts.

   It might also help to enable constituent inference in XTide.  This can
   be done from the [95]control panel or using the [96]infer setting.

  General tide related questions

   Q: I have a tide watch that only goes through the year 1999.  What year
   could I set it to that would be the same as this year?

   A: Sorry.  It just doesn't work like that.

   Q: Is there a set time advancement each day for the next high and low
   tide?  Does it always repeat 12 1/2 hours later?

   A: No.  The 12 hour 25 minute cycle is literally only a first-order
   approximation.  Most tide predictions involve twenty to thirty terms,
   and some require over a hundred.  The 12:25 cycle is just the most
   dominant term.

   Q: Somebody gave me a tide clock, but the instructions say it only
   works on the east coast.  How can this be?

   A: "Dumb" tide clocks assume that the 12 hour 25 minute cycle mentioned
   in the [97]previous question is a good enough approximation.  For the
   west coast, it isn't.  The following tide graphs illustrate the
   differences between east and west coast tides.  The high and low tide
   times that would be indicated by a "dumb" tide clock are shown with
   vertical yellow lines.  San Francisco shows a 2-hour discrepancy on the
   lower high tide.

   Emulation of dumb tide clock for Bangor, Maine

   Emulation of dumb tide clock for San Francisco, California

   Q: Why do the high and low tides have such different levels to them on
   any given day?  Does it actually coincide with the amount of pull
   exerted by the phase or closeness of the moon?

   A: The tides do not coincide too closely with the moon.  While the moon
   produces most of the force that drives them, the exact tide levels
   result from the sloshing around of huge amounts of water, the effects
   of the shape of the coastline, and things like that.

   Q: If it's high tide here, is it low tide in [faraway place]?

   A: It's hard to infer anything over large distances since localized
   effects can have a huge influence on tides.

   Q: What does the zero (0) on a tide chart represent?

   A: Tide heights are given relative to the "datum" which in most cases
   is one of several benchmarks corresponding to low tides of varying
   extremeness.  The preferred benchmark in the U.S. is Mean Lower Low
   Water (MLLW).  The odds of the predicted tide getting below MLLW on any
   given day are about half.  The preferred benchmark in the Netherlands
   is Mean Low Water Springs (MLWS).  MLWS is lower than MLLW.  The
   predicted tide will get below MLWS on average only about twice a
   month.  The preferred benchmark in Germany is Lowest Astronomical Tide
   (LAT).  LAT is the lowest tide predicted over a 19 year period.  The
   predicted tide will not get below LAT in that 19 year period, and is
   unlikely to get below it by any significant amount ever.

   In harmonics-dwf, some U.S. locations for which a MLLW benchmark was
   unavailable use an estimated value of MLLW that is derived from the
   predictions.  These estimates tend to yield predictions that differ
   from National Ocean Service published tables by (0.1-0.2) ft.  Older
   versions of harmonics-dwf used LAT for these stations, which of course
   yielded much larger discrepancies.

   For more information on datums, read the National Ocean Service
   publication [98]Tidal Datums and their Applications.

   Q: Why is it that the tides two miles from here are an hour different
   than the tides here?  If the tidal bulge follows the moon at 1,000
   miles per hour, how can the difference be so great?

   A: When the water tries to follow the moon, it runs up against a lot of
   obstacles, including its own inertia, the shape of the coastline, and
   the resonances that are set up by the continual tidal motion.  In some
   cases the tides are fighting a permanent current, e.g., going up a
   river, and this slows down the tidal crest.  The result is that the
   tides at any one place at any given time don't have a whole lot to do
   with the moon any more.

   Q: Why are there two high tides per day, anyway?  How is this possible?

   A: The standard simple answer to this question is that the water on the
   side of the earth opposite the moon bulges out due to decreased lunar
   gravity in the same way that the water on the side of the earth nearest
   the moon bulges out due to increased lunar gravity.  This is
   counter-intuitive in that one might expect all of the water to just
   rush over to the side where the moon is.  To explain this, I quote from
   "Our Restless Tides," a NOAA tutorial at
   [99]http://tidesandcurrents.noaa.gov/restles1.html:

     To all outward appearances, the moon revolves around the earth, but
     in actuality, the moon and earth revolve together around their
     common center of mass, or gravity.  The two astronomical bodies are
     held together by gravitational attraction, but are simultaneously
     kept apart by an equal and opposite centrifugal force produced by
     their individual revolutions around the center-of-mass of the
     earth-moon system.  This balance of forces in orbital revolution
     applies to the center-of-mass of the individual bodies only.  At the
     earth's surface, an imbalance between these two forces results in
     the fact that there exists, on the hemisphere of the earth turned
     toward the moon, a net (or differential) tide-producing force which
     acts in the direction of the moon's gravitational attraction, or
     toward the center of the moon.  On the side of the earth directly
     opposite the moon, the net tide-producing force is in the direction
     of the greater centrifugal force, or away from the moon.

   Q: What does "slack water" mean?

   A: This and many other terms are defined in the [100]NOAA tide
   glossary.

   Q: I have a theory that [random phenomenon] is related to tidal forces,
   but I am landlocked.  Can you, like, predict the "tides" for
   [landlocked location]?

   A: There is no support for this in XTide (ocean tides have only the
   vaguest connection to latitude, longitude, and the position of the
   moon), but you can find relevant information by searching the web for
   "land tide."

   Q: I want to write my own tide predicting program.  Can you provide a
   SIMPLE explanation of the tide-predicting function?

   A: The tide prediction function is fairly simple, requiring only a
   cosine function.  The piles of code surrounding it in XTide are to
   optimize the process of finding maxima and minima.  This can be done
   less optimally with significantly less code and effort (as early
   versions of XTide did).

   Since it is hard to draw summation symbols in ASCII, here is the
   pseudocode instead:

Height = Datum;
for a = 1 to numconst
  Height = Height +
    amplitude[a] * nodefactor[a] * cos (speed[a] * time + phase[a])
next a

   The datum is provided at the top of the data set in the harmonics.txt
   file.

   The amplitudes are the first column of numbers in the data set in the
   harmonics file.

   The node factors are tabulated for each year at the top of the
   harmonics file, or can be calculated from scratch using libcongen,
   available in the Congen package at
   [101]http://www.flaterco.com/xtide/files.html#experts.  Most likely you
   will just want to tabulate them.

   The speeds of the numconst constituents are listed at the top of the
   harmonics file in degrees per hour.

   If speed is in degrees or radians per X, then time is in X since the
   beginning of the year.  The specific time zone for the beginning of the
   year is chosen as described below.

   Phase includes a yearly adjustment called the equilibrium argument that
   is tabulated at the top of the harmonics file (or calculated from
   scratch like the node factors), minus the location-specific phases that
   are the second column of numbers in the data set (given in degrees).
   By default, you will get phases such that the time is measured from
   January 1 00:00 in the time zone specified by the meridian.
   Customarily, the meridian is chosen to be the standard time of the
   location in question to make life easier on simple tide prediction
   programs that don't mess with time zones or summer time adjustments.
   In the harmonics.txt file, you will find the meridian of each data set
   right before the time zone identifier, in hours and minutes:  e.g.,
   -05:00 :America/Montreal.  It is trivial to adjust the phases of the
   constituents for any desired meridian.  What XTide does is adjust them
   all to UTC and then use the Unix time zone functions to render the
   output with Daylight Savings Time and everything.

  Business questions

   Q: I want to license XTide so I can build a commercial product around
   it.

   A: XTide is released under the terms of the GNU General Public
   License.  [102]This FAQ about the GPL may be applicable to you.

   XTide has been used by commercial packages "at arm's length," to use
   the wording of the FAQ cited above, but I have never licensed it by any
   terms other than the GPL, nor have I ever offered any kind of warranty
   or service that one might expect if it were licensed commercially.

   PLEASE NOTE:  The question whether you can use XTide is completely
   separate from the question of whether you can use the tide data
   (harmonics files).  In general, data for U.S. ports are public domain,
   while others are for non-commercial use only.  [103]Read the
   boilerplate for details.

   Q: I have a lot of specific questions about the GNU General Public
   License and/or want a ruling that my specific plan is OK.

   A: Please read the GPL FAQ, available [104]here or [105]here.  If that
   does not answer your question, the people to ask are at
   [106]licensing@fsf.org.

   Q: We are a not-for-profit organization and we want to sell calendars
   with predictions from your web site.  Is that OK?

   A: Firstly, it's not my web site.  See [107]Question 1.  Secondly, all
   predictions for places outside the U.S. are for non-commercial use only
   (i.e. you can't sell them no matter what your tax status is).  Lastly,
   if you do want to sell calendars containing predictions for the U.S.,
   you must include all of the "NOT FOR NAVIGATION" disclaimers and agree
   to accept full liability in case someone has a problem.

   Legalities aside, my opinion has always been that people who are
   selling tide predictions have no business selling anything that is not
   directly certified by the [108]National Ocean Service.  Beggars can't
   be choosers, but when people are paying for something, they have a
   right to hold you to a higher standard.

   Q: I have a great idea to make money selling tide predictions, but I'm
   not good with technical stuff, so would you just do this for me...

   A: No.

   Q: I already make money selling tide prediction products, but your
   stuff is better, so would you just do this for me...

   A: No.

   Q: I need to do [poorly researched brainstorm having something to do
   with tide prediction]--how much would you charge in consulting fees to
   help me do it?

   A: It's moot.  Your plan won't work for one or more of the following
   reasons:
     * You think that it's possible to predict tides for arbitrary
       locations based on just the latitude and longitude.  It's not.
     * You are assuming that a database of quality-assured harmonic
       constants for ports worldwide is obtainable.  It isn't.  See
       [109]news about data maintenance and the [110]outside-the-U.S. FAQ
       for background.
     * The harmonic constants that you plan to use are encumbered in ways
       that make what you want to do with them illegal.
     * You think that harmonic constants can be burned into the firmware
       of an embedded device and never need maintenance.  They can't be;
       they need to be updated regularly.
     * You think that you can cut corners with a simple tide clock and
       still get tide predictions that match those published by NOAA.  You
       can't.

  Academic questions

   Q: How should I cite XTide within publications?

   A: The web site is the best thing you can cite.  For a general
   reference to XTide, I suggest the following, with the current date.

     [1]  David Flater.  XTide.  http://www.flaterco.com/xtide/.
     2005-07-04.

   If you are using specific predictions from XTide rather than just XTide
   in general, then you should cite the specific version of XTide and the
   specific data file that you used.  In this case, it would be
   appropriate to use the date indicated in the changelog for that version
   of XTide and the revision date of the data file.

     [2]  David Flater.  XTide version 2.8.2.
     http://www.flaterco.com/xtide/.  2005-01-06.

     [3]  harmonics-dwf-2005-06-05-v2.  Available from
     http://www.flaterco.com/xtide/files.html, 2005-06-05.

  Questions that you should have asked, but didn't

   Q: What is the difference between a reference station and a subordinate
   station?

   A: The following information was copied from [111]NOAA's web site on
   2007-02-17.

     The publication of full daily tide predictions is necessarily
     limited to a comparatively small number of stations.  These stations
     are referred to as "reference stations".  Tide predictions for more
     than 3000 other locations, referred to as "subordinate stations",
     can be obtained by applying specific differences to the daily tide
     predictions for one of the reference stations.  [...]

     Caution:  The time differences and height ratios used to calculate
     predictions at subordinate stations are derived from a comparison of
     simultaneous tide observations at the subordinate station and its
     reference station.  Because these adjustments are constant, they may
     not always provide for the daily variations in the actual tides,
     especially if the subordinate station is some distance from the
     reference station.  Therefore, although the application of time
     differences and height ratios will generally provide reasonably
     accurate approximations, they cannot result in predictions as
     accurate as those listed for the reference stations, which are based
     on much larger periods of analysis.

   In plain language, what you need to know is this:  All subordinate
   station predicions are approximate.  Tide predictions are always at
   best approximations of reality, but for subordinate stations that goes
   double.

   Q: These predictions are nonsense--what is going on here?

   Tide graph with a weird zigzag
2007-02-14 12:57 PM AKST   3.46 feet  High Tide
2007-02-14  3:00 PM AKST   Moonset
2007-02-14  7:08 PM AKST   Sunset
2007-02-14  9:06 PM AKST  -0.38 feet  Low Tide
2007-02-15  6:46 AM AKST   3.08 feet  Low Tide
2007-02-15  7:00 AM AKST   2.62 feet  High Tide
2007-02-15  9:07 AM AKST   Moonrise
2007-02-15  9:22 AM AKST   Sunrise
2007-02-15  1:46 PM AKST   3.46 feet  High Tide

   Current graph with weird double-flood
2004-03-31  5:01 AM PST  -0.64 knots  Max Ebb
2004-03-31  5:49 AM PST   Sunrise
2004-03-31 10:06 AM PST   0.02 knots  Max Flood
2004-03-31 10:18 AM PST   0.00 knots  Slack, Flood Begins
2004-03-31 11:21 AM PST  -0.00 knots  Slack, Ebb Begins
2004-03-31  1:01 PM PST   Moonrise
2004-03-31  4:13 PM PST  -0.90 knots  Max Ebb

   These are extreme examples of what can happen when the time differences
   and height ratios for subordinate stations don't "provide for the daily
   variations in the actual tides."  Although in the average case the
   offsets might yield good results, in extreme cases they can yield
   nonsense results like tide events happening in an impossible order or a
   "low" tide actually being higher than the "high" tide right next to
   it.  There is nothing XTide can do to rationalize these paradoxes, and
   the tide levels that are interpolated between paradoxical events are
   essentially garbage.

   Q: Where can I find tons of information about tides that is both more
   authoritative and better written than this FAQ?

   A: [112]http://tidesandcurrents.noaa.gov/education.html
     __________________________________________________________________

   [113]<- Previous [114]-> Next [115]Contents

References

   1. http://www.flaterco.com/xtide/bugs.html
   2. http://www.flaterco.com/xtide/design.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/faq.html#DST
   6. http://www.flaterco.com/xtide/faq.html#5
   7. http://www.flaterco.com/xtide/faq.html#40
   8. http://www.flaterco.com/xtide/faq.html#45
   9. http://www.flaterco.com/xtide/faq.html#20
  10. http://www.flaterco.com/xtide/faq.html#10
  11. http://www.flaterco.com/xtide/faq.html#onepage
  12. http://www.flaterco.com/xtide/faq.html#50
  13. http://www.flaterco.com/xtide/faq.html#duplicates
  14. http://www.flaterco.com/xtide/faq.html#51
  15. http://www.flaterco.com/xtide/faq.html#100
  16. http://www.flaterco.com/xtide/faq.html#nocurrents
  17. http://www.flaterco.com/xtide/faq.html#HistoricalPredictions
  18. http://www.flaterco.com/xtide/faq.html#60
  19. http://www.flaterco.com/xtide/faq.html#65
  20. http://www.flaterco.com/xtide/faq.html#70
  21. http://www.flaterco.com/xtide/faq.html#80
  22. http://www.flaterco.com/xtide/faq.html#90
  23. http://www.flaterco.com/xtide/faq.html#92
  24. http://www.flaterco.com/xtide/faq.html#93
  25. http://www.flaterco.com/xtide/faq.html#95
  26. http://www.flaterco.com/xtide/faq.html#100
  27. http://www.flaterco.com/xtide/faq.html#110
  28. http://www.flaterco.com/xtide/faq.html#130
  29. http://www.flaterco.com/xtide/faq.html#140
  30. http://www.flaterco.com/xtide/faq.html#150
  31. http://www.flaterco.com/xtide/faq.html#php
  32. http://www.flaterco.com/xtide/faq.html#210
  33. http://www.flaterco.com/xtide/faq.html#220
  34. http://www.flaterco.com/xtide/faq.html#250
  35. http://www.flaterco.com/xtide/faq.html#52
  36. http://www.flaterco.com/xtide/faq.html#170
  37. http://www.flaterco.com/xtide/faq.html#DumbTideClock
  38. http://www.flaterco.com/xtide/faq.html#160
  39. http://www.flaterco.com/xtide/faq.html#180
  40. http://www.flaterco.com/xtide/faq.html#190
  41. http://www.flaterco.com/xtide/faq.html#200
  42. http://www.flaterco.com/xtide/faq.html#230
  43. http://www.flaterco.com/xtide/faq.html#240
  44. http://www.flaterco.com/xtide/faq.html#255
  45. http://www.flaterco.com/xtide/faq.html#260
  46. http://www.flaterco.com/xtide/faq.html#55
  47. http://www.flaterco.com/xtide/faq.html#56
  48. http://www.flaterco.com/xtide/faq.html#calendar
  49. http://www.flaterco.com/xtide/faq.html#54
  50. http://www.flaterco.com/xtide/faq.html#300
  51. http://www.flaterco.com/xtide/faq.html#667
  52. http://www.flaterco.com/xtide/faq.html#cite
  53. http://www.flaterco.com/xtide/faq.html#refsub
  54. http://www.flaterco.com/xtide/faq.html#timewarp
  55. http://www.flaterco.com/xtide/faq.html#NOAA_education
  56. ftp://elsie.nci.nih.gov/pub/
  57. http://www.flaterco.com/xtide/sysreq.html#TZsysreq
  58. http://tbone.biol.sc.edu/tide/sitesel.html
  59. http://www.flaterco.com/xtide/
  60. http://tbone.biol.sc.edu/tide/sitesel.html
  61. http://www.flaterco.com/xtide/
  62. http://www.bsh.de/en/Marine%20data/Forecasts/Tides/index.jsp
  63. http://www.getij.nl/engels/
  64. http://www.hydro.linz.govt.nz/tides/majports/index.asp
  65. http://vannstand.statkart.no/Engelsk/skjema.php
  66. http://www.pol.ac.uk/ntslf/tides/
  67. http://easytide.ukho.gov.uk/
  68. http://tidesandcurrents.noaa.gov/tide_pred.html
  69. http://www.flaterco.com/xtide/harmonics.html
  70. http://www.flaterco.com/xtide/pound_to_fit.html
  71. http://www.flaterco.com/xtide/harmonics.html
  72. http://www.flaterco.com/xtide/harmonics.html
  73. http://topex-www.jpl.nasa.gov/mission/topex.html
  74. http://www.niwa.co.nz/services/tides
  75. http://sfports.wr.usgs.gov/SFPORTS/vec_map/vec_map.html
  76. http://tidesandcurrents.noaa.gov/
  77. http://www.noaa.gov/
  78. http://oceanservice.noaa.gov/
  79. http://tidesandcurrents.noaa.gov/ncop.html
  80. http://www.flaterco.com/xtide/time_t.html
  81. http://harmonics.unh.edu/xtide/files.html
  82. http://www.bodc.ac.uk/
  83. http://www.pol.ac.uk/
  84. http://flaterco.com/pol.html
  85. ftp://elsie.nci.nih.gov/pub/
  86. http://www.flaterco.com/xtide/installation.html#trouble
  87. mailto:dave@flaterco.com
  88. http://www.flaterco.com/xtide/bugs.html
  89. http://www.flaterco.com/xtide/settings.html
  90. http://www.flaterco.com/xtide/sysreq.html
  91. http://www.flaterco.com/xtide/ports.html
  92. http://www.almanaqueazul.org/?p=132
  93. http://tidesandcurrents.noaa.gov/tides07/
  94. http://www.flaterco.com/xtide/files.html#experts
  95. http://www.flaterco.com/xtide/advanced.html#cp
  96. http://www.flaterco.com/xtide/settings.html#infer
  97. http://www.flaterco.com/xtide/faq.html#170
  98. ftp://ftp.flaterco.com/xtide/tidal_datums_and_their_applications.pdf
  99. http://tidesandcurrents.noaa.gov/restles1.html
 100. ftp://ftp.flaterco.com/xtide/glossary2.pdf
 101. http://www.flaterco.com/xtide/files.html#experts
 102. http://www.gnu.org/licenses/gpl-faq.html#GPLInProprietarySystem
 103. http://www.flaterco.com/xtide/harmonics_boilerplate.txt
 104. http://www.fsf.org/licensing/licenses/gpl-faq.html
 105. http://www.gnu.org/licenses/gpl-faq.html
 106. mailto:licensing@fsf.org
 107. http://www.flaterco.com/xtide/faq.html#5
 108. http://oceanservice.noaa.gov/
 109. http://www.flaterco.com/xtide/news.html#datamaint
 110. http://www.flaterco.com/xtide/faq.html#60
 111. http://tidesandcurrents.noaa.gov/t2help.html
 112. http://tidesandcurrents.noaa.gov/education.html
 113. http://www.flaterco.com/xtide/bugs.html
 114. http://www.flaterco.com/xtide/design.html
 115. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Sunset over the bar, Bar Harbor, Maine, 1997-06-24

Design notes

  Principles

     * Portability
          + The scope is all "reasonably modern" flavors of Unix, X11, and
            C++
          + Limit language features to those that reliably compile
          + Respect the holy mantra "./configure; make; make install"
          + Allow trivial workarounds for platform- and
            distribution-specific bugs or special requirements
          + Disallow nontrivial workarounds and those that conflict with
            correct operation on non-broken platforms
     * Availability
          + Limit dependencies on external tools and libraries to those
            that are typically pre-installed
     * Usability
          + Maximize orthogonality of settings and switches
          + Support both interactive and non-interactive use
          + Command-line switches should be no more than two characters
            long
     * Maintainability
          + Accept no bogus patches
          + Maximize orthogonality of modules
     * Stability
          + Accept no bogus patches
          + Use no unstable tools or libraries
          + If it ain't broke, don't fix it
          + If it damages usability or maintainability, it's considered
            broke
          + Do not merely deprecate that which deserves to be deleted

   Some noteworthy violations:
     * Nontrivial workaround for platforms with obsolete zoneinfo
       databases
     * The -ns switch is deprecated but deserves to be deleted
     * libtcd painstakingly purged of bogosity

  Harmonics files

   XTide has a long history of harmonics file woes and has been through
   four different file formats trying to solve them.

        Readable Extensible Efficient Available
   TXT     X                              X
   XML               X                    X
   SQL               X          X
   TCD1                         X         X
   TCD2              X          X         X

   XTide 1 used a nice, human-readable text format (harmonics.txt) but it
   was neither efficient nor extensible.  New fields that were really,
   really necessary got wedged in as "hot comments," initiating a long
   downhill slide into architectural chaos.

   Unwisely, XTide 2 perpetuated the harmonics.txt format but added a new,
   extensible XML format for subordinate stations only (offsets.xml).  It
   was anticipated that one of two things would eventually happen:  either
   a reasonably functional and stable SQL database would become standard
   issue with the average Unix, obviating the need to avoid that external
   dependency, or harmonics.txt would go away and all stations would be
   done in extensible XML.  Neither one happened.  Migration to XML was
   put off repeatedly because it would exacerbate the performance
   bottleneck.

   Everybody suffered with the lousy performance until Jan Depner proposed
   to implement a binary format (TCD).  TCD1 fixed the performance problem
   but the extensibility problem persisted.  New fields could be added
   with just minor changes to libtcd, but then you needed to recompile the
   world.  Old versions of XTide couldn't read new harmonics files after
   fields were added.  This had a major chilling effect on all development
   that would have required new fields.

   TCD2 (a major, incompatible revision) emptied the queue of incompatible
   changes but also added a field whose content is extension fields
   encoded as text.  Adding fields this way is not as efficient as adding
   new binary fields, but it avoids the need to make an incompatible
   revision over small stuff.  The option to add new binary fields and
   bump the major rev remains open should that become necessary.

  Known problems

   Lots of serious design problems were fixed in refactorings begining
   with version 2.7 (early 2004) and continuing through version 2.9.
   Remaining minor problems:
    1. The interface with X11 is still weird, especially bootstrapping.
    2. The analog tide clock icon caused more problems (with buggy window
       managers) than it was worth.
    3. URLs assigned to prediction pages by the web server should probably
       be based on the harmonics file name and the location name rather
       than a transient "row ID."
    4. Constituent inference was patched in via libtcd and maybe could
       have been integrated better.  In theory, you might want to control
       it on a station-by-station basis like preferred units, and it
       probably should not require a station reload to turn it on or off.
    5. Graph and calendar modes are implemented by transient classes.
       These are not proper objects, but they are too complicated to be
       implemented with methods alone.

  C++ feature footprint

   At the time XTide 2 was developed, the fancier features of C++ such as
   the Standard Template Library (STL) and exceptions did not work in a
   portable fashion among the commonly available compilers, so their use
   was avoided.  Similarly, [5]Qt and other free alternatives to Motif
   were not widely available, so Athena Widgets were used.  The resulting
   interface may seem [6]primitive by today's standards, but it still
   works.

   By the time of the 2.7 refactorings, the STL appeared to be stable and
   widely available, so standard templates were introduced where
   appropriate to simplify new code.  Old code was not STLified until the
   Great Cleanup of 2006 (XTide 2.9).

   The long long int data type was introduced in XTide 2.6 as part of the
   changes to handle dates before 1970 and after 2037.  Nobody complained.

   Streams were expunged from XTide 2.6 after compilers started
   deprecating XTide's use of them.  In XTide, C++ streams did not add
   value versus plain old C I/O, but this is not the case for every
   application.

   The bool data type was introduced in XTide 2.9.

   Exceptions are still not used, but probably could be, as those
   compilers that don't support them don't support the Standard Template
   Library either.

  Coding conventions

   A uniform coding convetion was imposed in XTide 2.9.  See the file
   CodingConventions.txt included in the distribution tarball.
     __________________________________________________________________

   [7]<- Previous [8]-> Next [9]Contents

References

   1. http://www.flaterco.com/xtide/faq.html
   2. http://www.flaterco.com/xtide/credits.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.trolltech.com/
   6. http://www.catb.org/~esr/jargon/html/S/stone-knives-and-bearskins.html
   7. http://www.flaterco.com/xtide/faq.html
   8. http://www.flaterco.com/xtide/credits.html
   9. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

   [4]Moonrise over Marginal Way

Bibliography

   Canonical sources on the NOS tide prediction methodology (including a
   mathematical explanation from first principles in SP98):

     Manual of Harmonic Analysis and Prediction of Tides.  Special
     Publication No. 98, Revised (1940) Edition (reprinted 1958 with
     corrections; reprinted again 1994).  United States Government
     Printing Office, 1994.

     Computer Applications to Tides in the National Ocean Survey.
     Supplement to Manual of Harmonic Analysis and Prediction of Tides
     (Special Publication No. 98).  National Ocean Service, National
     Oceanic and Atmospheric Administration, U.S. Department of Commerce,
     January 1982.

   Those can be ordered from NOAA for $5 or $10, depending on the phase of
   the moon.

   Miscellaneous publications available from
   [5]http://www.flaterco.com/xtide/files.html#pubs:

     [6]Tide and Current Glossary.  National Ocean Service, January
     2000.  Downloaded from [7]NOS, 2003-12-19.

     [8]Tidal Datums and their Applications.  NOAA Special Publication
     NOS CO-OPS 1, June 2000.  Downloaded from [9]NOS, 2004-08-27.

     [10]Nathaniel Bowditch, LL.D.  The American Practical Navigator:  An
     Epitome of Navigation.  NIMA Pub. No. 9, Bicentennial Edition,
     2002.  Downloaded from [11]NGA, 2004-09-28.  42 MB.  Chapter 9 is a
     tutorial on tides and currents.

   My sources for X-windows programming reference:

     Kimball, Paul E.  The X Toolkit Cookbook.  Prentice Hall P T R, New
     Jersey, 1995.

     Nye, Adrian.  Xlib Programming Manual.  O'Reilly & Associates, Inc.,
     Volume 1, Third Edition, July 1993.

   A catalog of information on the ISO 8601 standard date and time
   notation can be found at
   [12]http://dmoz.org/Science/Reference/Standards/Individual_Standards/IS
   O_8601/.

   iCalendar format and usage is according to [13]RFC 2445 and [14]RFC
   2446, with some hints taken from [15]RFC 2447 (November 1998).

   An article about a model-based approach to tide prediction, which is
   completely different from what XTide does, is

     Derek Goring, "Computer Models Define Tide Variability," The
     Industrial Physicist, v. 7, n. 5, October/November 2001, pp. 14-17.
     Available at
     [16]http://www.niwa.co.nz/rc/prog/chaz/news/tidalmodel.pdf or
     [17]http://www.aip.org/tip/INPHFA/vol-7/iss-5/p14.pdf.

   Michael Foreman's publications are a good read if you are interested in
   the Doodson approach to tide prediction.

     Foreman, M.G.G., 1977.  Manual for Tidal Heights Analysis and
     Prediction.  Pacific Marine Science Report 77-10, Institute of Ocean
     Sciences, Patricia Bay, Sidney, B.C., 58 pp. (2004 revision).

     Foreman, M.G.G., 1978.  Manual for Tidal Currents Analysis and
     Predition.  Pacific Marine Science Report 78-6, Institute of Ocean
     Sciences, Patricia Bay, Sidney, B.C., 57 pp. (2004 revision).

     Foreman, M.G.G., and R.F. Henry, 1979.  Tidal Analysis Based on High
     and Low Water Observations.  Pacific Marine Science Report 79-15,
     Institute of Ocean Sciences, Patricia Bay, Sidney, B.C., 36 pp.
     (2004 revision).

   Miscellaneous publications mentioned by Hugh Casement that I haven't
   read:

     On the response method of tide prediction, which is completely
     different and allegedly better than what XTide does:  Munk, Walter
     H.; Cartwright, David E.:  Tidal spectroscopy and prediction.
     Philosophical Transactions of the Royal Society, A 259 (1966).

     An interesting-sounding publication that Hugh Casement hasn't read
     either:  Horn, Walter:  Some recent approaches to tidal problems
     (Centre Belge d'Ocans, Brussels, year unknown).

     Horn, Walter:  Tafeln der Astronomischen Argumente V0 und der
     Korrektionen j, v (Deutsches Hydrographisches Institut, Hamburg,
     1967).

     Doodson, in Proceedings of the Royal Society A.100 (London, 1921).

     Cartwright and Tayler, in Geophysical Journal of the Royal
     Astronomical Society 23 (1971).

     Jean Meeus, Astronomical Algorithms, Willmann-Bell.
     __________________________________________________________________

   [18]<- Previous [19]-> Next [20]Contents

References

   1. http://www.flaterco.com/xtide/credits.html
   2. http://www.flaterco.com/xtide/time_t.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/
   5. http://www.flaterco.com/xtide/files.html#pubs
   6. ftp://ftp.flaterco.com/xtide/glossary2.pdf
   7. http://www.tidesandcurrents.noaa.gov/pub.html
   8. ftp://ftp.flaterco.com/xtide/tidal_datums_and_their_applications.pdf
   9. http://www.tidesandcurrents.noaa.gov/pub.html
  10. ftp://ftp.flaterco.com/xtide/Bowditch.pdf
  11. http://pollux.nss.nga.mil/pubs/pubs_j_apn_sections.html?rid=187
  12. http://dmoz.org/Science/Reference/Standards/Individual_Standards/ISO_8601/
  13. http://www.flaterco.com/xtide/rfc2445.txt
  14. http://www.flaterco.com/xtide/rfc2446.txt
  15. http://www.flaterco.com/xtide/rfc2447.txt
  16. http://www.niwa.co.nz/rc/prog/chaz/news/tidalmodel.pdf
  17. http://www.aip.org/tip/INPHFA/vol-7/iss-5/p14.pdf
  18. http://www.flaterco.com/xtide/credits.html
  19. http://www.flaterco.com/xtide/time_t.html
  20. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents

Appendix A -- Historical predictions and Y2038 compliance

   As of 2002, the average Unix uses a signed 32-bit integer to represent
   time as a count of seconds since 1970-01-01 00:00:00Z.  The limits of
   that representation are 1901-12-13 20:45:52Z and 2038-01-19 03:14:07Z.
   Some platforms instead use an unsigned 32-bit integer while others
   already use 64-bit integers.

   XTide originally limited itself to the range 1970 to 2037.  This
   provided portability and reliable results regardless of the time_t
   representation and allowed Interval (the difference between two
   timestamps) to be represented using a signed 32-bit integer.  However,
   an increasing number of requests for historical "past predictions"
   combined with slow progress in migrating the average Unix platform to a
   time representation capable of surviving year 2038 finally motivated
   the incorporation of a workaround.

   If XTide is compiled with this workaround, time_t is redefined as a
   signed 64-bit integer and the platform's time functions are bypassed.
   Years from 1 to 4000 are allowed.  However, time zones and daylight
   savings time are sacrificed.  Everything becomes UTC. [4]*

   In XTide 2.9 and newer, the workaround can be enabled at configure time
   using configure --enable-time-workaround.  The range of years that is
   selectable in timestamp dialogs is automatically expanded to 1700 to
   2100 when the time workaround is enabled.  If a different range is
   required, the definitions of Global::dialogFirstYear and
   Global::dialogLastYear in Global.cc must be changed manually.

   In order to obtain predictions for past and future years, it is also
   necessary to use a harmonics file that supports those years.  The new
   harmonics file harmonics-dwf, rev. 2004-10-05 or later, supports the
   years 1700 to 2100.  If you need to extend the range of years further,
   use the following procedure.
    1. Obtain and build the most recent versions of Congen, Tcd-utils and
       Harmbase2, available at
       [5]http://www.flaterco.com/xtide/files.html.  You will also need to
       install the version of Postgres indicated by the Harmbase2
       instructions.
    2. Obtain the most recent Postgres database dump of harmonics-dwf from
       the same place and load it:  createdb harmbase2; psql harmbase2 <
       harmonics-dwf-*.sql.
    3. Export the database to a new TCD file using the export program of
       Harmbase2, specifying whatever years you wanted:  export -b 1700 -e
       2300 harmonics-me.

   If you are using .txt and .xml files, you can extend the range of years
   as follows.
    1. Obtain and build the most recent versions of Congen and Tcd-utils,
       available at [6]http://www.flaterco.com/xtide/files.html.
    2. Generate the needed years as explained in the README in the Congen
       distribution.  E.g., congen -a1 -b 1700 -e 2300 < congen_input.txt
       > out.txt.
    3. Using a text editor, edit harmonics.txt and replace the segment
       between "Begin congen output" and "End congen output" with the
       congen output that you just generated.
    4. Convert the data to TCD format using build_tide_db as explained in
       the README of the Tcd-utils distribution.

   Please be aware that extrapolating predictions over large spans of time
   may give extremely inaccurate results.  Don't even go there until you
   [7]read this FAQ about it.

   * The time scale used by the time workaround is not strictly speaking
   UTC since it does not implement [8]leap seconds, but neither does the
   standard library.  See [9]Limitation #6.
     __________________________________________________________________

   [10]<- Previous [11]-> Next [12]Contents

References

   1. http://www.flaterco.com/xtide/bibliography.html
   2. http://www.flaterco.com/xtide/mincurrents.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/time_t.html#leap
   5. http://www.flaterco.com/xtide/files.html
   6. http://www.flaterco.com/xtide/files.html
   7. http://www.flaterco.com/xtide/faq.html#57
   8. http://www.boulder.nist.gov/timefreq/pubs/bulletin/leapsecond.htm
   9. http://www.flaterco.com/xtide/bugs.html
  10. http://www.flaterco.com/xtide/bibliography.html
  11. http://www.flaterco.com/xtide/mincurrents.html
  12. http://www.flaterco.com/xtide/xtide.html#contents

################################################################

   [1]<- Previous [2]-> Next [3]Contents
   [4]About harmonic constants and sub station corrections
   [5]Change log

Appendix B -- Application of offsets for Min Flood and Min Ebb events

   [6]B.1  Background
   [7]B.2  Secondary Station Adjustments Instructions (NOS)
   [8]B.3  Comparison of old and new results
   [9]B.4  Comparison with published tables

  Background

   XTide distinguishes the following common events for current stations:

   Max Flood           Maximum current in the flood (+) direction.
   Max Ebb             Maximum current in the ebb ( -) direction.
   Slack, Flood Begins Zero current preceding flood.
   Slack, Ebb Begins   Zero current preceding ebb.

   Additionally, it distinguishes two events that are not seen as
   frequently:

   Min Flood Minimum current in the flood (+) direction between two Max
   Floods when the current never crosses zero.
   Min Ebb Minimum current in the ebb ( -) direction between two Max Ebbs
   when the current never crosses zero.

   In XTide 2.8, a change was made to the application of offsets for Min
   Flood and Min Ebb events.

   Event XTide 2.7 time adjust XTide 2.7 current adjust XTide 2.8 time
   adjust XTide 2.8 current adjust
   Min Flood Same as Max Ebb Same as Max Ebb Same as Slack, Flood Begins;
   if null, use Max Flood Same as Max Flood
   Min Ebb Same as Max Flood Same as Max Flood Same as Slack, Ebb Begins;
   if null, use Max Ebb Same as Max Ebb

   This change was made based on a reading of the highlighted sections of
   the National Ocean Service web page quoted below, which was downloaded
   from [10]http://co-ops.nos.noaa.gov/currents04/t2chelp.html on
   2004-09-15.

   The second highlighted passage states that no attempt is made to
   predict the speed of the minimum currents.  It would not make sense for
   XTide to leave these values unadjusted because a very small ratio could
   cause the supposed maxima to have lower amplitude than the minimum.
   Applying the ratio used for the surrounding maxima will give reasonable
   looking results as long as the adjustment is only a ratio.  (Additive
   adjustments would not produce reasonable results.)
     __________________________________________________________________

           BEGIN NATIONAL OCEAN SERVICE TEXT (highlighting added)
     __________________________________________________________________

                 Secondary Station Adjustments Instructions

   The publication of full daily predictions is necessarily limited to a
   comparatively small number of stations. These stations are referred to
   as "reference stations". Tidal current predictions for more than 2500
   other locations can be obtained by applying certain differences to the
   daily predictions for the reference stations.

   These pages provide a listing of the more than 2500 "subordinate
   stations" for which such predictions can be made, the differences and
   ratios to be used, and a link to the appropriate reference station. The
   stations in the listing are arranged geographically to make it possible
   to find stations which are available for an area you are interested in.

   Since all tidal current stations are located offshore, many of them are
   named for the channels, rivers, and inlets they are located in, or for
   cities, towns, or navigational points they are located near. Some
   personal knowledge of the area you are interested in may be necessary
   to determine which station(s) are most appropriate for your use.

   Depths: Although current measurements may have been recorded at various
   depths in the past, the data listed here for most subordinate stations
   are mean values determined to have been representative of the current
   at each location. For that reason, no specific current meter depth for
   those stations are given. Beginning with the Boston Harbor tidal
   current survey in 1971, data for individual meter depths were published
   and subsequent new data may be presented in a similar manner.

   Since most of the current data in these pages came from meters
   suspended from survey vessels or anchored buoys, the listed depths are
   those measured downward from the surface. Some later data have come
   from meters anchored at fixed depths from the bottom. These meter
   positions were defined as depth below chart datum. Such defined depths
   in these pages will be accompanied by the small letter "d".

   Minimum Currents: The user may note that at many locations the current
   may not diminish to a true slack water or zero speed stage. For that
   reason, the phrases, "minimum before flood" and "minimum before ebb"
   are used in these pages rather than "slack water" although either or
   both minimums may actually reach a zero speed value at some locations.

   Maximum Currents: Near the coast and in inland waters, the current
   increases from a minimum current (slack water) for a period of about 3
   hours until the maximum speed or strength of the current is reached.
   The speed then decreases for another period of about 3 hours when
   minimum current is again reached and the current begins a similar cycle
   in the opposite direction. The current that flows towards the coast or
   up a stream is known as the flood current; the opposite flow is known
   as the ebb current. Speeds of the current at reference stations are
   listed as positive values for floods and negative values for ebbs.
   These pages list the average directions of the maximum floods and
   maximum ebb currents. The directions listed are given in degrees, true,
   reading from 000 at north to 359 and are the directions toward which
   the current flow.

   Differences and Speed Ratios: These pages contain time differences by
   which the user can compile approximate times for the minimum and
   maximum current phases at the subordinate stations. Time differences
   for those phases should be applied to the corresponding phases at the
   reference station. It will be seen upon inspection that some
   subordinate stations exhibit either a double flood or a double ebb
   stage, or both. In those cases, a separate time difference is listed
   for each of the three flood (or ebb) phases and should be applied only
   to the maximum flood (or ebb) phase at the reference station. The
   results obtained by the application of time differences will be based
   upon the local time meridian. Differences of time meridians between a
   subordinate stations and its reference station have been accounted for.

   The speed ratios are used to compile approximations of the daily
   current speeds at the subordinate stations and refer only to the
   maximum floods and ebbs. No attempt is made to predict the speed of the
   minimum currents. These ratios are multiplied to the corresponding
   maximum current phases at the reference station. As mentioned before,
   however, some stations may exhibit either a double flood or a double
   ebb, or both. As with time differences, separate ratios are listed for
   each of the three flood (or ebb) phases and should be applied only to
   the daily maximum flood (or ebb) speed at the reference station. It
   should be noted that although the speed of a given current phase at a
   subordinate station is obtained by reference to the corresponding phase
   at a reference station, the directions of the current at the two places
   may differ considerably. These pages list the average directions of the
   maximum current phases at the subordinate stations.

   Example Tidal Current Calculations

   For Cape May Channel, the time and speed adjustments listed in the
   tables are:
Minimum       Minimum         Speed
Before Flood  Before  Ebb     Ratio
Flood         Ebb           Flood Ebb
-1 14  -1 30  -1 11  -0 45   1.1  1.8

   and the reference station is Delaware Bay Entrance. If the times and
   speeds listed in column 1 are the minimum and maximum tidal currents
   for a day at Delaware Bay Entrance, column 2 are the time corrections,
   and column 3 are the speed corrections; column 4 will be the predicted
   currents at Cape May Channel. These values are computed by adding or
   subtracting the times in column 1 to the adjustments in column 2; and
   by multiplying the speeds in column 1 by the ratios in column 3.
     (1)                 (2)        (3)         (4)
  Times     Speed                            Times     Speed
0114  0425   1.3    -1 14  -1 30   *1.1    0000  0255   1.4
0736  1055  -1.3    -1 11  -0 45   *1.8    0625  1010  -2.3
1351  1650   1.2    -1 14  -1 30   *1.1    1237  1520   1.3
1958  2316  -1.3    -1 11  -0 45   *1.8    1847  2231  -2.3
     __________________________________________________________________

                       END NATIONAL OCEAN SERVICE TEXT
     __________________________________________________________________

  Comparison of old and new results

   From [11]http://co-ops.nos.noaa.gov/currents04/tab2pc2.html
   (2004-09-15):
                                                              Minimum       Mini
mum         Speed    Direction
                                                              Before Flood  Befo
re  Ebb     Ratio    At Maximum
Station                                              Depth    Flood         Ebb
          Flood Ebb  Flood Ebb  Reference Station
Admiralty Head, 0.5 mile west of                              -0 31  -0 03  +0 0
1  -0 07   1.3  1.2   145  025  Admiralty Inlet

   Resulting XTide data set:

   Name
Admiralty Head, 0.5 mile west of, Washington Current

   Reference
Admiralty Inlet, Washington Current

   Max time add
-00:03

   Max level add
NULL

   Max level mult
1.300

   Min time add
-00:07

   Min level add
NULL

   Min level mult
1.200

   Flood begins
-00:31

   Ebb begins
+00:01

   NOS predictions for 2004-09-08 and 2004-09-09 at reference station,
   from [12]http://co-ops.nos.noaa.gov/currents04/ADMIRALI.shtml
   (2004-09-15):
    Slack    Maximum   Slack    Maximum   Slack    Maximum   Slack    Maximum
Slack    Maximum
    Water    Current   Water    Current   Water    Current   Water    Current
Water    Current
Day  Time  Time  Veloc  Time  Time  Veloc  Time  Time  Veloc  Time  Time  Veloc
 Time  Time  Veloc
     h.m.  h.m.  knots  h.m.  h.m.  knots  h.m.  h.m.  knots  h.m.  h.m.  knots
 h.m.  h.m.  knots

  8         402   -2.3   814  1122    1.5  1449  1801   -1.2        2257   -0.1
  9         508   -2.4   909  1219    1.7  1543  1856   -1.5

   Corresponding XTide results:

   Reference station Sub station (XTide 2.7) Sub station (XTide 2.8)
2004-09-08  4:02 AM PDT  -2.33 knots  Max Ebb
2004-09-08  8:13 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-08 11:22 AM PDT   1.51 knots  Max Flood
2004-09-08  2:48 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-08  6:01 PM PDT  -1.22 knots  Max Ebb
2004-09-08 10:57 PM PDT  -0.07 knots  Min Ebb
2004-09-09  5:08 AM PDT  -2.36 knots  Max Ebb
2004-09-09  9:08 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-09 12:19 PM PDT   1.71 knots  Max Flood
2004-09-09  3:42 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-09  6:56 PM PDT  -1.47 knots  Max Ebb
2004-09-09 11:22 PM PDT   0.00 knots  Slack, Flood Begins

2004-09-08  3:55 AM PDT  -2.80 knots  Max Ebb
2004-09-08  7:42 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-08 11:19 AM PDT   1.96 knots  Max Flood
2004-09-08  2:49 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-08  5:54 PM PDT  -1.47 knots  Max Ebb
2004-09-08 10:54 PM PDT  -0.09 knots  Min Ebb
2004-09-09  5:01 AM PDT  -2.84 knots  Max Ebb
2004-09-09  8:37 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-09 12:16 PM PDT   2.22 knots  Max Flood
2004-09-09  3:43 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-09  6:49 PM PDT  -1.77 knots  Max Ebb
2004-09-09 10:51 PM PDT   0.00 knots  Slack, Flood Begins

2004-09-08  3:55 AM PDT  -2.80 knots  Max Ebb
2004-09-08  7:42 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-08 11:19 AM PDT   1.96 knots  Max Flood
2004-09-08  2:49 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-08  5:54 PM PDT  -1.47 knots  Max Ebb
2004-09-08 10:58 PM PDT  -0.08 knots  Min Ebb
2004-09-09  5:01 AM PDT  -2.84 knots  Max Ebb
2004-09-09  8:37 AM PDT   0.00 knots  Slack, Flood Begins
2004-09-09 12:16 PM PDT   2.22 knots  Max Flood
2004-09-09  3:43 PM PDT  -0.00 knots  Slack, Ebb Begins
2004-09-09  6:49 PM PDT  -1.77 knots  Max Ebb
2004-09-09 10:51 PM PDT   0.00 knots  Slack, Flood Begins
     __________________________________________________________________

  Comparison with published tables

   When the change in XTide's behavior was made in 2004, the NOS web site
   did not provide calculated predictions at the subordinate stations for
   comparison.  Upon reviewing the issue in 2007 (at which time those
   predictions were available), it was found that the published tables did
   neither of the behaviors that were implemented in XTide.

   CAPTION: Time offsets applied to Min Ebb event

   XTide 2.7     XTide 2.8      NOS 2007
     Flood   Minimum Before Ebb   Ebb

   Whereas the behavior of the published tables seemed to be in conflict
   with the [13]Secondary Station Adjustments Instructions, it was
   resolved not to change the behavior of XTide at that time.

    Reference station

   NOS table copied from
   [14]http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=6030
   +Admiralty+Inlet&fldavgd=179&ebbavgd=003&footnote= 2007-02-24

        Admiralty Inlet
   Predicted Tidal Current     March, 2007
   Flood Direction, 179 True.  Ebb (-)Direction, 003 True.
   NOAA, National Ocean Service

     Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current
   Day Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots
   12 0049 0347 -0.9   0825 -0.1   1458 -2.4 1917 2229 +1.5
   13 0207 0512 -1.0   0948 -0.2   1610 -2.4 2019 2335 +1.8

   Comparable XTide output, using harmonics-rmk-20040615.tcd
   tide -l"admiralty inlet" -b"2007-03-12 00:00" -e"2007-03-14 00:00" -mc
   -empSsMm -tf"%H%M" -fh

   Day Slack Flood
   Slack
   Ebb Slack Flood
   Slack
   Mon 12 0048 0347 -0.93 kt
   0824 -0.08 kt
   1457 -2.41 kt 1916 2229 1.52 kt
   Tue 13 0206 0512 -1.04 kt
   0948 -0.18 kt
   1610 -2.45 kt 2018 2335 1.75 kt

    Subordinate station

Name             Agate Pass, North End of, Washington Current
Reference        Admiralty Inlet, Washington Current
Min time add     -0:59
Min level add    NULL
Min level mult   0.700
Max time add     -1:00
Max level add    NULL
Max level mult   0.800
Flood begins     -1:28
Ebb begins       -0:18

   NOS table copied from
   [15]http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=6030
   +Admiralty+Inlet&secstn=Agate+Passage,+north+end&sbfh=%2D1&sbfm=28&fldh
   =%2D1&fldm=00&sbeh=%2D0&sbem=18&ebbh=%2D0&ebbm=59&fldr=0.8&ebbr=0.7&fld
   avgd=230&ebbavgd=032&footnote= 2007-02-24

        Agate Passage, north end
   Predicted Tidal Current      March, 2007
   Flood Direction, 230 True.   Ebb (-)Direction, 032 True.
   NOAA, National Ocean Service

     Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current Slack
   Water Maximum
   Current
   Day Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots Time
   h.m. Time
   h.m. Veloc
   knots
   12 0031 0248 -0.6   0726 -0.1   1359 -1.7 1749 2129 +1.2
   13 0149 0413 -0.7   0849 -0.1   1511 -1.7 1851 2235 +1.4

   Comparable XTide output, using harmonics-rmk-20040615.tcd
   tide -l"Agate Pass, North End of, Washington Current" -b"2007-03-12
   00:00" -e"2007-03-14 00:00" -mc -empSsMm -tf"%H%M" -fh

   Day Slack Flood
   Slack
   Ebb Slack Flood
   Slack
   Mon 12 0030 0248 -0.65 kt
   0806 -0.06 kt
   1358 -1.69 kt 1748 2129 1.21 kt
   Tue 13 0148 0413 -0.73 kt
   0930 -0.13 kt
   1511 -1.71 kt 1850 2235 1.40 kt
     __________________________________________________________________

   [16]<- Previous [17]-> Next [18]Contents
   [19]About harmonic constants and sub station corrections
   [20]Change log

References

   1. http://www.flaterco.com/xtide/time_t.html
   2. http://www.flaterco.com/xtide/pound_to_fit.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/harmonics.html
   5. http://www.flaterco.com/xtide/changelog.html#2.8
   6. http://www.flaterco.com/xtide/mincurrents.html#background
   7. http://www.flaterco.com/xtide/mincurrents.html#instructions
   8. http://www.flaterco.com/xtide/mincurrents.html#oldnew
   9. http://www.flaterco.com/xtide/mincurrents.html#tables
  10. http://co-ops.nos.noaa.gov/currents04/t2chelp.html
  11. http://co-ops.nos.noaa.gov/currents04/tab2pc2.html
  12. http://co-ops.nos.noaa.gov/currents04/ADMIRALI.shtml
  13. http://www.flaterco.com/xtide/mincurrents.html#instructions
  14. http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=6030+Admiralty+Inlet&fldavgd=179&ebbavgd=003&footnote=
  15. http://tidesandcurrents.noaa.gov/get_predc.shtml?year=2007&stn=6030+Admiralty+Inlet&secstn=Agate+Passage,+north+end&sbfh=%2D1&sbfm=28&fldh=%2D1&fldm=00&sbeh=%2D0&sbem=18&ebbh=%2D0&ebbm=59&fldr=0.8&ebbr=0.7&fldavgd=230&ebbavgd=032&footnote=
  16. http://www.flaterco.com/xtide/time_t.html
  17. http://www.flaterco.com/xtide/pound_to_fit.html
  18. http://www.flaterco.com/xtide/xtide.html#contents
  19. http://www.flaterco.com/xtide/harmonics.html
  20. http://www.flaterco.com/xtide/changelog.html#2.8

################################################################

   [1]<- Previous [2]-> Next [3]Contents
   [4]Modes and formats
   [5]FAQ

Appendix C -- Making calendars fit onto a single page

  Get rid of unwanted information

   Regardless of which format you are using, having extra stuff in the
   calendar that you don't want isn't going to help.  If you are using a
   web page somewhere, look for options that allow you to suppress sun and
   moon events or control the formatting of timestamps.  If you are using
   XTide directly, you do this using the eventmask and timefmt settings.
   The following examples assume command line usage, but you can change
   settings in several other ways.  See [6]settings for details.

   To get rid of unwanted columns for sun and moon events, use the -em
   command line switch to set an event mask.  E.g, to suppress all sun and
   moon events, set the event mask to the value pSsMm.  p = phase of moon,
   S = sunrise, s = sunset, M = moonrise, m = moonset.

   To get rid of unwanted verbosity in timestamps (AM/PM and/or time
   zone), use the -tf command line switch to set the time format string.
   E.g., to reduce it to four digits of 24-hour notation, set the time
   format string to %H%M.  To keep AM/PM but lose the time zone, set the
   time format string to %l:%M %p.

  Scale down HTML

   If the calendar that you want to print is on a web page, the next step
   is to set up your print scaling to make it fit on the page without a
   lot of ugly text wrapping.  The process for doing this is slightly
   different depending on your browser and operating system.

    Firefox 1.5.0.1 Linux

   Access the print scaling menu via File -> Page Setup.  On the Format &
   Options tab, unselect Shrink To Fit Page Width and specify an arbitrary
   shrink factor.  Try various shrink factors and see how they look in
   File -> Print Preview.  Print when you find one you like.

   The Format & Options tab also lets you choose between Portrait and
   Landscape printing, which can be helpful depending on whether your
   calendar is really long or really wide.

    Firefox 1.5.0.1 Windows XP

   Do File -> Print Preview.  Use the controls at the top of the window to
   select Portrait or Landscape printing and to scale down the HTML until
   it fits nicely on a page.  When ready, select Print.

    Internet Explorer 6 Windows XP

   Internet Explorer 6 does not support print scaling.  No wonder so many
   Windows users had trouble printing calendars!  Doh!  (Smack forehead.)

   Some Windows printer drivers add an option for print scaling on a
   buried menu, but what that does is not what you need.

    Internet Explorer 7 Windows XP

   The following instructions are based on Microsoft's documentation.  I
   cannot test these instructions because IE7 installation fails on my PC.

    1. Click the arrow to the right of the Print button, and then click
       Print Preview.
    2. Pull down the print size menu ( Shrink To Fit ) and try different
       options until the calendar fits nicely on a page.
    3. When ready, click on the tiny printer icon to print.

  Get serious--use LaTeX

   The problem with printing calendars from HTML is that HTML doesn't know
   anything about typesetting printed documents.  HTML has no concept of
   pagination.  Whether the result ends up on one page or three when you
   print it was never supposed to be a concern.

   The right language to use in this case is LaTeX.  Like HTML, LaTeX is a
   markup language, but it is all about typesetting printed documents.

   XTide can generate calendars in LaTeX format.  These can be converted
   to PDFs using pdflatex, and those PDFs can then be printed on any size
   paper using Acrobat Reader.

   If you are using XTide through a web page, you just have to hunt for an
   option to generate a PDF and hope that there is one.

   The process to generate and view a PDF from the command line is as
   follows:
bash-3.00$ tide -l"Location Name" -mc -fl -b"Start Time" -e"End Time" > cal.tex
bash-3.00$ pdflatex cal.tex
bash-3.00$ acroread cal.pdf

   The default page geometry in LaTeX mode is probably not optimal for
   making your calendar look nice.  Experiment with different values for
   pageheight (-ph 420) and pagewidth (-pw 297) until the calendar looks
   nice in PDF.  Do not worry that the shape of the pages in the PDF is
   not what you have in your printer.

   [7]example of nicely formatted calendar

   When you are happy with the look of the PDF, do the following to print
   it.

    Acrobat Reader 7.0 Linux

   Use the File -> Print Setup menu of Acrobat Reader to select Portrait
   or Landscape printing, then on the File -> Print menu check off Shrink
   oversized pages to paper size and Expand small pages to paper size.

   Issue:  I have experienced disappearing lines when printing via the HP
   DeskJet 5550 driver of CUPS 1.1.23.  This problem does not occur when
   printing under Windows XP, so clearly there is some print option that I
   am missing.

    Acrobat Reader 7.0 Windows XP

   Use the File -> Print Setup menu of Acrobat Reader to select Portrait
   or Landscape printing, then on the File -> Print menu, change Page
   Scaling to Fit to Printer Margins.
     __________________________________________________________________

   [8]<- Previous [9]-> Next [10]Contents
   [11]Modes and formats
   [12]FAQ

References

   1. http://www.flaterco.com/xtide/mincurrents.html
   2. http://www.flaterco.com/xtide/xtide1diff.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/modes.html
   5. http://www.flaterco.com/xtide/faq.html#onepage
   6. http://www.flaterco.com/xtide/settings.html
   7. http://www.flaterco.com/xtide/BarHarbor.pdf
   8. http://www.flaterco.com/xtide/mincurrents.html
   9. http://www.flaterco.com/xtide/xtide1diff.html
  10. http://www.flaterco.com/xtide/xtide.html#contents
  11. http://www.flaterco.com/xtide/modes.html
  12. http://www.flaterco.com/xtide/faq.html#onepage

################################################################

   [1]<- Previous [2]-> Next [3]Contents

Icon Differences from XTide 1

   XTide 2 is a complete redesign of XTide 1.  There are too many subtle
   improvements to list them all, but here are the not so subtle ones:
     * New interactive user interface for X windows client
     * Integrated web server now provided in distribution
     * Simpler, better command line interface
     * Handles multiple harmonics files transparently
     * Subordinate stations are now stored in an external database and are
       expanded to handle all known styles of offsets
     * Hydraulic currents are fixed
     * Removed useless options and modes
     * Added sun and moon information (by popular demand...)
     * Fast, efficient binary format for harmonics data

   These are the non-obvious things you must know in order to migrate:
    1. The environment variable HFILE is no longer used to specify the
       harmonics file; instead, HFILE_PATH is used:

export HFILE_PATH=/usr/local/share/xtide/harmonics.tcd

       If HFILE_PATH is not set, XTide looks for the file "harmonics.tcd"
       in the default directory.
    2. XTide now has its own built-in icon.  Remove any icon settings that
       you made in your window manager init files.
    3. You may no longer use anonymous units in harmonics files.  The
       units must be one of the recognized alternatives.  These are:
       feet, meters, knots, knots^2 (for hydraulic currents).  If you are
       still using an ancient harmonics file that contains no units or
       "bogo-knots," then shame on you.  It's high time that you upgraded.
     __________________________________________________________________

   [4]<- Previous [5]-> Next [6]Contents

References

   1. http://www.flaterco.com/xtide/pound_to_fit.html
   2. http://www.flaterco.com/xtide/quickinst.html
   3. http://www.flaterco.com/xtide/xtide.html#contents
   4. http://www.flaterco.com/xtide/pound_to_fit.html
   5. http://www.flaterco.com/xtide/quickinst.html
   6. http://www.flaterco.com/xtide/xtide.html#contents