Provided by: gmt-common_5.2.1+dfsg-3build1_all 
NAME
grdcut - Extract subregion from a grid
SYNOPSIS
grdcut ingrid outgrid region [ [nodata] ] [ [n]lon/lat/radius[unit] ] [ [level] ] [ [n|r]min/max ] [
-f<flags> ]
Note: No space is allowed between the option flag and the associated arguments.
DESCRIPTION
grdcut will produce a new outgrid file which is a subregion of ingrid. The subregion is specified with -R
as in other programs; the specified range must not exceed the range of ingrid (but see -N). If in doubt,
run grdinfo to check range. Alternatively, define the subregion indirectly via a range check on the node
values or via distances from a given point. Complementary to grdcut there is grdpaste, which will join
together two grid files along a common edge.
REQUIRED ARGUMENTS
ingrid This is the input grid file.
-Goutgrid
This is the output grid file.
OPTIONAL ARGUMENTS
-N[nodata]
Allow grid to be extended if new -R exceeds existing boundaries. Append nodata value to
initialize nodes outside current region [Default is NaN].
-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest. This defines the subregion to be cut out.
-S[n]lon/lat/radius[unit]
Specify an origin and radius; append a distance unit (see UNITS) and we determine the
corresponding rectangular region so that all grid nodes on or inside the circle are contained in
the subset. If -Sn is used we set all nodes outside the circle to NaN.
-V[level] (more ...)
Select verbosity level [c].
-Z[n|r]min/max
Determine the new rectangular region so that all nodes outside this region are also outside the
given z-range [-inf/+inf]. To indicate no limit on min or max, specify a hyphen (-). Normally, any
NaNs encountered are simply skipped and not considered in the decision. Use -Zn to consider a NaN
to be outside the z-range. This means the new subset will be NaN-free. Alternatively, use -Zr to
consider NaNs to be within the data range. In this case we stop shrinking the boundaries once a
NaN is found [Default simply skips NaNs when making the range decision].
-f[i|o]colinfo (more ...)
Specify data types of input and/or output columns.
-^ 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 FILE FORMATS
By default GMT writes out grid as single precision floats in a COARDS-complaint netCDF file format.
However, GMT is able to produce grid files in many other commonly used grid file formats and also
facilitates so called "packing" of grids, writing out floating point data as 1- or 2-byte integers. To
specify the precision, scale and offset, the user should add the suffix =id[/scale/offset[/nan]], where
id is a two-letter identifier of the grid type and precision, and scale and offset are optional scale
factor and offset to be applied to all grid values, and nan is the value used to indicate missing data.
In case the two characters id is not provided, as in =/scale than a id=nf is assumed. When reading
grids, the format is generally automatically recognized. If not, the same suffix can be added to input
grid file names. See grdconvert and Section grid-file-format of the GMT Technical Reference and Cookbook
for more information.
When reading a netCDF file that contains multiple grids, GMT will read, by default, the first
2-dimensional grid that can find in that file. To coax GMT into reading another multi-dimensional
variable in the grid file, append ?varname to the file name, where varname is the name of the variable.
Note that you may need to escape the special meaning of ? in your shell program by putting a backslash in
front of it, or by placing the filename and suffix between quotes or double quotes. The ?varname suffix
can also be used for output grids to specify a variable name different from the default: "z". See
grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical Reference and Cookbook
for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids.
GEOGRAPHICAL AND TIME COORDINATES
When the output grid type is netCDF, the coordinates will be labeled "longitude", "latitude", or "time"
based on the attributes of the input data or grid (if any) or on the -f or -R options. For example, both
-f0x -f1t and -R90w/90e/0t/3t will result in a longitude/time grid. When the x, y, or z coordinate is
time, it will be stored in the grid as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH
in the gmt.conf file or on the command line. In addition, the unit attribute of the time variable will
indicate both this unit and epoch.
EXAMPLES
Suppose you have used surface to grid ship gravity in the region between 148E - 162E and 8N - 32N, and
you do not trust the gridding near the edges, so you want to keep only the area between 150E - 160E and
10N - 30N, then:
gmt grdcut grav_148_162_8_32.nc -Ggrav_150_160_10_30.nc -R150/160/10/30 -V
To return the subregion of a grid such that any boundary strips where all values are entirely above 0 are
excluded, try
gmt grdcut bathy.nc -Gtrimmed_bathy.nc -Z-/0 -V
To return the subregion of a grid that contains all nodes within a distance of 500 km from the point
45,30 try
gmt grdcut bathy.nc -Gsubset_bathy.nc -S45/30/500k -V
SEE ALSO
gmt, grdclip, grdpaste, grdinfo
COPYRIGHT
2015, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe