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<HTML>
<HEAD>
<TITLE>grdfilter</TITLE>
</HEAD>
<BODY>
<H1>grdfilter</H1>
<HR>
<PRE>
<!-- Manpage converted by man2html 3.0.1 -->
grdfilter - Filter a <I>.grd</I> file in the Time domain
</PRE>
<H2>SYNOPSIS</H2><PRE>
<B>grdfilter</B> <I>input</I><B>_</B><I>file.grd</I> <B>-D</B><I>flag</I> <B>-F</B><I><type><width></I> <B>-G</B><I>out</I>
<I>put</I><B>_</B><I>file.grd</I> [ <B>-I</B><I>x</I><B>_</B><I>inc</I>[<B>m|c</B>][/<I>y</I><B>_</B><I>inc</I>[<B>m|c</B>]] ] [
<B>-R</B><I>west/east/south/north</I>[<I>r</I>] ] [ <B>-T</B> ] [ <B>-V</B> ]
</PRE>
<H2>DESCRIPTION</H2><PRE>
<B>grdfilter</B> will filter a <I>.grd</I> file in the time domain using
a boxcar, cosine arch, gaussian, median, or mode filter
and computing distances using Cartesian or Spherical
geometries. The output <I>.grd</I> file can optionally be gener
ated as a sub<B>-R</B>egion of the input and/or with a new
<B>-I</B>ncrement. In this way, one may have "extra space" in the
input data so that the edges will not be used and the out
put can be within one-half- width of the input edges. If
the filter is low-pass, then the output may be less fre
quently sampled than the input.
<I>input</I><B>_</B><I>file.grd</I>
The file of points to be filtered.
<B>-D</B> Distance <I>flag</I> tells how grid (x,y) relates to fil
ter <I>width</I> as follows:
<I>flag</I> = 0: grid (x,y) same units as <I>width</I>, Cartesian
distances.
<I>flag</I> = 1: grid (x,y) in degrees, <I>width</I> in kilome
ters, Cartesian distances.
<I>flag</I> = 2: grid (x,y) in degrees, <I>width</I> in km, dx
scaled by cos(middle y), Cartesian distances.
The above options are fastest because they allow
weight matrix to be computed only once. The next
two options are slower because they recompute
weights for each East-West scan line.
<I>flag</I> = 3: grid (x,y) in degrees, <I>width</I> in km, dx
scaled by cosine(y), Cartesian distance calcula
tion.
<I>flag</I> = 4: grid (x,y) in degrees, <I>width</I> in km,
Spherical distance calculation.
<B>-F</B> Choose one only of <B>bcgmp</B> for (<B>b</B>)oxcar, (<B>c</B>)osine
Arch, (<B>g</B>)aussian, (<B>m</B>)edian, or maximum likelihood
(<B>p</B>)robability (a mode estimator) filter and specify
full <I>width</I>.
<B>-G</B> <I>output</I><B>_</B><I>file.grd</I> is the output of the filter.
</PRE>
<H2>OPTIONS</H2><PRE>
<B>-I</B> <I>x</I><B>_</B><I>inc</I> [and optionally <I>y</I><B>_</B><I>inc</I>] is the output Incre
integer multiples of the old ones (in the input
data), filtering will be considerably slower.
[Default: Same as input.]
<B>-R</B> <I>west,</I> <I>east,</I> <I>south,</I> and <I>north</I> defines the Region of
the output points. [Default: Same as input.]
<B>-T</B> Toggle the node registration for the output grid so
as to become the opposite of the input grid
[Default gives the same registration as the input
grid].
<B>-V</B> Selects verbose mode, which will send progress
reports to stderr [Default runs "silently"].
</PRE>
<H2>EXAMPLES</H2><PRE>
Suppose that north_pacific_dbdb5.grd is a file of 5 minute
bathymetry from 140E to 260E and 0N to 50N, and you want
to find the medians of values within a 300km radius (600km
full width) of the output points, which you choose to be
from 150E to 250E and 10N to 40N, and you want the output
values every 0.5 degree. Using spherical distance calcula
tions, you need:
grdfilter north_pacific_dbdb5.grd <B>-G</B>filtered_pacific.grd
<B>-Fm</B>600 <B>-D</B>4 <B>-R</B>150/250/10/40 <B>-I</B>0.5 <B>-V</B>
</PRE>
<H2>SEE ALSO</H2><PRE>
<I>gmt</I>(l), <I><A HREF="grdfft.html">grdfft</A></I>(l)
</PRE>
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