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<HTML>
<HEAD>
<TITLE>nearneighbor</TITLE>
</HEAD>
<BODY>
<H1>nearneighbor</H1>
<HR>
<PRE>
<!-- Manpage converted by man2html 3.0.1 -->
nearneighbor - A "Nearest neighbor" gridding algorithm
</PRE>
<H2>SYNOPSIS</H2><PRE>
<B>nearneighbor</B> [ <I>xyzfile(s)</I> ] <B>-G</B><I>out</I><B>_</B><I>grdfile</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>-N</B><I>sectors</I>
<B>-R</B><I>west/east/south/north</I>[<B>r</B>] <B>-S</B><I>search</I><B>_</B><I>radius</I>[<B>m|c|k|K</B>] [
<B>-E</B><I>empty</I> ] [ <B>-F</B> ] [ <B>-H</B>[<I>nrec</I>] ] [ <B>-L</B>[<I>flag</I>] ] [ <B>-V</B> ] [ <B>-W</B> ] [
<B>-:</B> ] [ <B>-bi</B>[<B>s</B>][<I>n</I>] ]
</PRE>
<H2>DESCRIPTION</H2><PRE>
<B>nearneighbor</B> reads arbitrarily located (x,y,z[,w]) triples
[quadruplets] from standard input [or <I>xyzfile(s)</I>] and uses
a nearest neighbor algorithm to assign an average value to
each node that have one or more points within a radius
centered on the node. The average value is computed as a
weighted mean of the nearest point from each sector inside
the search radius. The weighting function used is w(r) =
1.0 / (1 + d ^ 2), where d = 3 * r / search_radius and r
is distance from the node. This weight is modulated by the
observation points' weights [if supplied].'
<I>xyzfile(s)</I>
3 [or 4, see <B>-W</B>] column ASCII file(s) [or binary,
see <B>-b</B>] holding (x,y,z[,w]) data values. If no file
is specified, <B>nearneighbor</B> will read from standard
input.
<B>-G</B> Give the name of the output grdfile.
<B>-I</B> <I>x</I><B>_</B><I>inc</I> [and optionally <I>y</I><B>_</B><I>inc</I>] is the grid spacing.
Append <B>m</B> to indicate minutes or <B>c</B> to indicate sec
onds.
<B>-N</B> The circular area centered on each node is divided
into several sectors. Average values will only be
computed if there is at least one value inside each
of the sectors for a given node. Nodes that fail
this test are assigned the value NaN (but see <B>-E</B>).
[Default is quadrant search, i.e., <I>sectors</I> = 4].
Note that only the nearest value per sector enters
into the averaging, not all values inside the cir
cle.
<B>-R</B> <I>west,</I> <I>east,</I> <I>south,</I> and <I>north</I> specify the Region of
interest. To specify boundaries in degrees and min
utes [and seconds], use the dd:mm[:ss] format.
Append <B>r</B> if lower left and upper right map coordi
nates are given instead of wesn.
<B>-S</B> Sets the <I>search</I><B>_</B><I>radius</I> in same units as the grid
spacing; append <B>m</B> to indicate minutes or <B>c</B> to indi
cate seconds. Append <B>k</B> to indicated km (implies <B>-R</B>
flat Earth].
</PRE>
<H2>OPTIONS</H2><PRE>
<B>-E</B> Set the value assigned to empty nodes [NaN].
<B>-F</B> Force pixel registration. [Default is grid regis
tration].
<B>-H</B> Input file(s) has Header record(s). Number of
header records can be changed by editing your .gmt
defaults file. If used, <B><A HREF="GMT.html">GMT</A></B> default is 1 header
record. Not used with binary data.
<B>-L</B> Boundary condition <I>flag</I> may be <I>x</I> or <I>y</I> or <I>xy</I> indi
cating data is periodic in range of x or y or both
set by <B>-R</B>, or <I>flag</I> may be <I>g</I> indicating geographical
conditions (x and y are lon and lat). [Default is
no boundary conditions]. If no flag is given, it
is assumed that the x column contains longitudes,
which may differ from the region in <B>-R</B> by [multi
ples of] 360 degrees [Default assumes no periodic
ity].
<B>-V</B> Selects verbose mode, which will send progress
reports to stderr [Default runs "silently"].
<B>-:</B> Toggles between (longitude,latitude) and (lati
tude,longitude) input/output. [Default is (longi
tude,latitude)]. Applies to geographic coordinates
only.
<B>-W</B> Input data have a 4th column containing observation
point weights. These are multiplied with the geo
metrical weight factor to determine the actual
weights used in the calculations.
<B>-bi</B> Selects binary input. Append <B>s</B> for single precision
[Default is double]. Append <I>n</I> for the number of
columns in the binary file(s). [Default is 3 (or 4
if <B>-W</B> is set) columns].
</PRE>
<H2>EXAMPLES</H2><PRE>
To create a gridded data set from the file sea
MARCII_bathy.lon_lat_z using a 0.5 min grid, a 5 km search
radius, using an octant search, and set empty nodes to
-9999, try
nearneighbor seaMARCII_bathy.lon_lat_z <B>-R</B>242/244/-22/-20
<B>-I</B>.5<B>m</B> <B>-E</B>-9999 <B>-G</B>bathymetry.grd <B>-S</B>5k <B>-N</B>8
To make a global gridded file from the data in geoid.xyz
using a 1 degree grid, a 200 km search radius, spherical
nearneighbor geoid.xyz <B>-R</B>0/360/-90/90 <B>-I</B>1 <B>-L</B>g <B>-G</B>geoid.grd
<B>-S</B>20K <B>-N</B>4
</PRE>
<H2>SEE ALSO</H2><PRE>
<I><A HREF="blockmean.html">blockmean</A></I>(l), <I><A HREF="blockmedian.html">blockmedian</A></I>(l), <I><A HREF="blockmode.html">blockmode</A></I>(l), <I>gmt</I>(l), <I>sur</I>
<I>face</I>(l), <I><A HREF="triangulate.html">triangulate</A></I>(l)
</PRE>
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