This is the command grdcutgmt that can be run in the OnWorks free hosting provider using one of our multiple free online workstations such as Ubuntu Online, Fedora Online, Windows online emulator or MAC OS online emulator
grdcut - Extract subregion from a grid
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.
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.
ingrid This is the input grid file.
This is the output grid file.
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.
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
-V[level] (more ...)
Select verbosity level [c].
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
Print GMT version and exit.
Print full path to GMT share directory and exit.
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.
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
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