nearneighborgmt - Online in the Cloud

PROGRAM:

NAME

nearneighbor - "Grid table data using a ""Nearest neighbor"" algorithm"

SYNOPSIS

nearneighbor [ table ] out_grdfile increment sectors[/min_sectors] region [
search_radius[unit] [ empty ] [ [level] ] [ ] [ -bi<binary> ] [ -di<nodata> ] [ -f<flags>
] [ -h<headers> ] [ -i<flags> ] [ -n<flags> ] [ -r ] [ -:[i|o] ]

Note: No space is allowed between the option flag and the associated arguments.

DESCRIPTION

nearneighbor reads arbitrarily located (x,y,z[,w]) triples [quadruplets] from standard
input [or table] 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 / (1 + d ^ 2), where d = 3 * r /
search_radius and r is distance from the node. This weight is modulated by the weights of
the observation points [if supplied].

REQUIRED ARGUMENTS

-Gout_grdfile
Give the name of the output grid file.

-Ixinc[unit][=|+][/yinc[unit][=|+]]
x_inc [and optionally y_inc] is the grid spacing. Optionally, append a suffix
modifier. Geographical (degrees) coordinates: Append m to indicate arc minutes or s
to indicate arc seconds. If one of the units e, f, k, M, n or u is appended
instead, the increment is assumed to be given in meter, foot, km, Mile, nautical
mile or US survey foot, respectively, and will be converted to the equivalent
degrees longitude at the middle latitude of the region (the conversion depends on
PROJ_ELLIPSOID). If /y_inc is given but set to 0 it will be reset equal to x_inc;
otherwise it will be converted to degrees latitude. All coordinates: If = is
appended then the corresponding max x (east) or y (north) may be slightly adjusted
to fit exactly the given increment [by default the increment may be adjusted
slightly to fit the given domain]. Finally, instead of giving an increment you may
specify the number of nodes desired by appending + to the supplied integer
argument; the increment is then recalculated from the number of nodes and the
domain. The resulting increment value depends on whether you have selected a
gridline-registered or pixel-registered grid; see App-file-formats for details.
Note: if -Rgrdfile is used then the grid spacing has already been initialized; use
-I to override the values.

-Nsectors[/min_sectors]
The circular area centered on each node is divided into sectors sectors. Average
values will only be computed if there is at least one value inside each of at least
min_sectors of the sectors for a given node. Nodes that fail this test are assigned
the value NaN (but see -E). If min_sectors is omitted it is set to be at least 50%
of sectors (i.e., rounded up to next integer). [Default is a quadrant search with
100% coverage, i.e., sectors = min_sectors = 4]. Note that only the nearest value
per sector enters into the averaging; the more distant points are ignored.

-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest.

-Ssearch_radius[unit]
Sets the search_radius that determines which data points are considered close to a
node. Append the distance unit (see UNITS).

OPTIONAL ARGUMENTS

table 3 [or 4, see -W] column ASCII file(s) [or binary, see -bi] holding (x,y,z[,w]) data
values. If no file is specified, nearneighbor will read from standard input.

-Eempty
Set the value assigned to empty nodes [NaN].

-V[level] (more ...)
Select verbosity level [c].

-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.

-bi[ncols][t] (more ...)
Select native binary input. [Default is 3 (or 4 if -W is set) columns].

-dinodata (more ...)
Replace input columns that equal nodata with NaN.

-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.

-h[i|o][n][+c][+d][+rremark][+rtitle] (more ...)
Skip or produce header record(s).

-icols[l][sscale][ooffset][,...] (more ...)
Select input columns (0 is first column).

-n[b|c|l|n][+a][+bBC][+tthreshold]
Append +bBC to set any boundary conditions to be used, adding g for geographic, p
for periodic, or n for natural boundary conditions. For the latter two you may
append x or y to specify just one direction, otherwise both are assumed. [Default
is geographic if grid is geographic].

-r (more ...)
Set pixel node registration [gridline].

-:[i|o] (more ...)
Swap 1st and 2nd column on input and/or output.

-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows
use just -).

-+ or just +
Print an extensive usage (help) message, including the explanation of any
module-specific option (but not the GMT common options), then exits.

-? or no arguments
Print a complete usage (help) message, including the explanation of options, then
exits.

--version
Print GMT version and exit.

--show-datadir
Print full path to GMT share directory and exit.

UNITS

For map distance unit, append unit d for arc degree, m for arc minute, and s for arc
second, or e for meter [Default], f for foot, k for km, M for statute mile, n for nautical
mile, and u for US survey foot. By default we compute such distances using a spherical
approximation with great circles. Prepend - to a distance (or the unit is no distance is
given) to perform "Flat Earth" calculations (quicker but less accurate) or prepend + to
perform exact geodesic calculations (slower but more accurate).

GRID VALUES PRECISION

Regardless of the precision of the input data, GMT programs that create grid files will
internally hold the grids in 4-byte floating point arrays. This is done to conserve memory
and furthermore most if not all real data can be stored using 4-byte floating point
values. Data with higher precision (i.e., double precision values) will lose that
precision once GMT operates on the grid or writes out new grids. To limit loss of
precision when processing data you should always consider normalizing the data prior to
processing.

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 with 100% sector coverage, and set empty
nodes to -9999:

gmt nearneighbor seaMARCII_bathy.lon_lat_z -R242/244/-22/-20 -I0.5m \
-E-9999 -Gbathymetry.nc -S5k -N8/8

To make a global grid file from the data in geoid.xyz using a 1 degree grid, a 200 km
search radius, spherical distances, using an quadrant search, and set nodes to NaN only
when fewer than two quadrants contain at least one value:

gmt nearneighbor geoid.xyz -R0/360/-90/90 -I1 -Lg -Ggeoid.nc -S200k -N4

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