grdcut(1) GMT grdcut(1)
NAME
grdcut - Extract subregion from a grid
SYNOPSIS
grdcut ingrid -Goutgrid
-Rregion [ -N[nodata] ] [ -S[n]lon/lat/radius[unit] ] [ -V[level] ]
[ -Z[n|r]min/max ] [ -fflags ]
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 indi-
rectly 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].
-Rxmin/xmax/ymin/ymax[+r][+uunit] (more a|)
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 sub-
set. If -Sn is used we set all nodes outside the circle to NaN.
-V[level] (more a|)
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. Alterna-
tively, 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 a|)
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 just use -).
-+ or just +
Print an extensive usage (help) message, including the explana-
tion 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 all options, then exits.
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 aFlat Eartha 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 apackinga of grids, writing out floating point
data as 1- or 2-byte integers. (more a|)
GEOGRAPHICAL AND TIME COORDINATES
When the output grid type is netCDF, the coordinates will be labeled
alongitudea, alatitudea, or atimea 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 dis-
tance of 500 km from the point 45,30 try
gmt grdcut bathy.nc -Gsubset_bathy.nc -S45/30/500k -V
SEE ALSO
gmt(1), grdclip(1), grdinfo(1), grdpaste(1), surface(1)
COPYRIGHT
2017, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
5.4.2 Jun 24, 2017 grdcut(1)
gmt5 5.4.2 - Generated Wed Jun 28 18:17:16 CDT 2017