.TH NEARNEIGHBOR l DATE
.SH NAME
nearneighbor \- A "Nearest neighbor" gridding algorithm
.SH SYNOPSIS
\fBnearneighbor\fP [ \fIxyzfile(s)\fP ] \fB\-G\fP\fIout_grdfile\fP \fB\-I\fP\fIx_inc\fP[m|c][/\fIy_inc\fP[m|c]]  
\fB\-N\fP\fIsectors\fP \fB\-R\fP\fIwest/east/south/north\fP[\fIr\fP] \fB\-S\fP\fIsearch_radius\fP[m|c] 
[ \fB\-E\fP\fIempty\fP ] [ \fB\-F\fP ] [ \fB\-H\fP ] [ \fB\-M\fP ] [ \fB\-V\fP ] [ \fB\-W\fP ] [ \fB\-:\fP ] [ \fB\-b\fP[\fBd\fP] ]
.SH DESCRIPTION
\fBnearneighbor\fP reads arbitrarily located (x,y,z[, w]) triples [quadruplets]
from standard input [or \fIxyzfile(s)\fP] 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 all points inside the search radius.  The
weighting function used is w(r) = 1.0 / (1 + d * d), where d = 3 * r / search_radius and r is
distance from the node.  This weight is modulated by the observation points' weights [if supplied].
.TP
\fIxyzfile(s)\fP
3 [or 4, see \fB\-W\fP] column ASCII file(s) [or binary, see \fB\-b\fP] holding (x,y,z[,w]) data values.  If no file is specified, \fBnearneighbor\fP
will read from standard input.
.TP
.B \-G
Give the name of the output grdfile.
.TP
.B \-I
\fIx_inc\fP [and optionally \fIy_inc\fP] is the block size. Append m to indicate minutes, c to indicate seconds.
.TP
.B \-N
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 \fB\-E\fP).  [Default is quadrant
search, i.e., \fIsectors\fP = 4].
#include "explain_-R.txt"
.TP
.B \-S
Sets the \fIsearch_radius\fP.  In same units as the grid spacing (but see \fB\-M\fP).  Append m to indicate minutes, c to indicate seconds.
.SH OPTIONS
.TP
.B \-E
Set the value assigned to empty nodes [NaN].
.TP
.B \-F
Force pixel registration.  [Default is grid registration].
#include "explain_-H.txt"
Not used with binary data.
.TP
.B \-M
Use map units, i.e., input data and grid spacings are in degrees of longitude and latitude,
and \fIsearch_radius\fP is in km.
#include "explain_-V.txt"
#include "explain_-t.txt"
.TP
.B \-W
Input data have a 4th column containing observation point weights.  These are multiplied
with the geometrical weight factor to determine the actual weights used in the calculations.
.TP
.B \-b
Selects binary input mode  [Default is ASCII].
Append \fBd\fP to indicate double precision for binary data [Default is single].
.SH EXAMPLES
.sp
To create a gridded data set from the file seaMARCII_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
.sp
nearneighbor seaMARCII_bathy.lon_lat_z \fB\-R\fP242/244/-22/-20 \fB\-I\fP.5m \fB\-E\fP-9999 \fB\-G\fPbathymetry.grd
\fB\-S\fP5 \fB\-N\fP8
.SH SEE ALSO
blockmean, blockmedian, gmt, surface, triangulate
#include "refs.i"
