NEARNEIGHBOR

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NAME

nearneighbor - A "Nearest neighbor" gridding algorithm  

SYNOPSIS

nearneighbor [ xyzfile(s) ] -Gout_grdfile -Ix_inc[m|c][/y_inc[m|c]] -Nsectors -Rwest/east/south/north[r] -Ssearch_radius[m|c] [ -Eempty ] [ -F ] [ -H ] [ -M ] [ -V ] [ -W ] [ -: ] [ -b[d] ]  

DESCRIPTION

nearneighbor reads arbitrarily located (x,y,z[, w]) triples [quadruplets] from standard input [or xyzfile(s)] 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].
xyzfile(s)
3 [or 4, see -W] column ASCII file(s) [or binary, see -b] holding (x,y,z[,w]) data values. If no file is specified, nearneighbor will read from standard input.
-G
Give the name of the output grdfile.
-I
x_inc [and optionally y_inc] is the block size. Append m to indicate minutes, c to indicate seconds.
-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 -E). [Default is quadrant search, i.e., sectors = 4]. #include "explain_-R.txt"
-S
Sets the search_radius. In same units as the grid spacing (but see -M). Append m to indicate minutes, c to indicate seconds.
 

OPTIONS

-E
Set the value assigned to empty nodes [NaN].
-F
Force pixel registration. [Default is grid registration]. #include "explain_-H.txt" Not used with binary data.
-M
Use map units, i.e., input data and grid spacings are in degrees of longitude and latitude, and search_radius is in km. #include "explain_-V.txt" #include "explain_-t.txt"
-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.
-b
Selects binary input mode [Default is ASCII]. Append d to indicate double precision for binary data [Default is single].
 

EXAMPLES

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

nearneighbor seaMARCII_bathy.lon_lat_z -R242/244/-22/-20 -I.5m -E-9999 -Gbathymetry.grd -S5 -N8  

SEE ALSO

blockmean, blockmedian, gmt, surface, triangulate #include "refs.i"


 

Index

NAME
SYNOPSIS
DESCRIPTION
OPTIONS
EXAMPLES
SEE ALSO

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Time: 07:11:08 GMT, January 07, 2025