nearneighbor - A "Nearest neighbor" gridding algorithm
nearneighbor [ xyzfile(s) ] -Gout_grdfile -Ix_inc[m|c][/y_inc[m|c]]
-Nsectors -Rwest/east/south/north[r] -Ssearch_radius[m|c|k|K] [ -Eempty
] [ -F ] [ -H[nrec] ] [ -Lflag ] [ -V ] [ -W ] [ -: ] [ -bi[s][n] ] [
nearneighbor reads arbitrarily located (x,y,z[,w]) triples [quadru-
plets] 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 com-
puted 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 sup-
3 [or 4, see -W] column ASCII file(s) [or binary, see -b] hold-
ing (x,y,z[,w]) data values. If no file is specified, nearneigh-
bor will read from standard input.
-G Give the name of the output grdfile.
-I x_inc [and optionally y_inc] is the grid spacing. Append m to
indicate minutes or 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]. Note that
only the nearest value per sector enters into the averaging, not
all values inside the circle.
-R xmin, xmax, ymin, and ymax specify the Region of interest. For
geographic regions, these limits correspond to west, east,
south, and north and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
and upper right map coordinates are given instead of wesn. The
two shorthands -Rg -Rd stand for global domain (0/360 or
-180/+180 in longitude respectively, with -90/+90 in latitude).
For calendar time coordinates you may either give relative time
(relative to the selected TIME_EPOCH and in the selected
TIME_UNIT; append t to -JX|x), or absolute time of the form
[date]T[clock] (append T to -JX|x). At least one of date and
clock must be present; the T is always required. The date string
must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
yyyy[-Www[-d]] (ISO week calendar), while the clock string must
be of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be as indicated (however, input/output
and plotting formats are flexible).
-S Sets the search_radius in same units as the grid spacing; append
m to indicate minutes or c to indicate seconds. Append k to
indicated km (implies -R and -I are in degrees); use uppercase K
if distances should be calculated using great circles [k uses
-E Set the value assigned to empty nodes [NaN].
-F Force pixel registration. [Default is grid registration].
-H Input file(s) has Header record(s). Number of header records can
be changed by editing your .gmtdefaults4 file. If used, GMT
default is 1 header record. Use -Hi if only input data should
have header records [Default will write out header records if
the input data have them]. Not used with binary data.
-L Boundary condition flag may be x or y or xy indicating data is
periodic in range of x or y or both set by -R, or flag may be g
indicating geographical conditions (x and y are lon and lat).
[Default is no boundary conditions].
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-: Toggles between (longitude,latitude) and (latitude,longitude)
input and/or output. [Default is (longitude,latitude)]. Append
i to select input only or o to select output only. [Default
-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 Selects binary input. Append s for single precision [Default is
double]. Append n for the number of columns in the binary
[Default is 3 (or 4 if -W is set) columns].
-f Special formatting of input and output columns (time or geo-
graphical data) Specify i(nput) or o(utput) [Default is both
input and output]. Give one or more columns (or column ranges)
separated by commas. Append T (Absolute calendar time), t (time
relative to chosen TIME_EPOCH), x (longitude), y (latitude), g
(geographic coordinate), or f (floating point) to each column or
column range item.
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:
nearneighbor seaMARCII_bathy.lon_lat_z -R242/244/-22/-20 -I.5m -E-9999
-Gbathymetry.grd -S5k -N8
To make a global gridded 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 empty nodes to NaN, run
nearneighbor geoid.xyz -R0/360/-90/90 -I1 -Lg -Ggeoid.grd -S20K -N4
blockmean(l), blockmedian(l), blockmode(l), gmt(l), surface(l), trian-
GMT4.0 1 Oct 2004 NEARNEIGHBOR(l)
Man(1) output converted with