1GRDCUT(1) GMT GRDCUT(1)
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6 grdcut - Extract subregion from a grid
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9 grdcut ingrid -Goutgrid
10 -Rregion [ -N[nodata] ] [ -S[n]lon/lat/radius[unit] ] [ -V[level] ]
11 [ -Z[n|r]min/max ] [ -fflags ]
12 Note: No space is allowed between the option flag and the associated
14 arguments.
15
17 grdcut will produce a new outgrid file which is a subregion of ingrid.
18 The subregion is specified with -R as in other programs; the specified
19 range must not exceed the range of ingrid (but see -N). If in doubt,
20 run grdinfo to check range. Alternatively, define the subregion indi‐
21 rectly via a range check on the node values or via distances from a
22 given point. Complementary to grdcut there is grdpaste, which will join
23 together two grid files along a common edge.
24
26 ingrid This is the input grid file.
27 -Goutgrid
29 This is the output grid file.
30
32 -N[nodata]
33 Allow grid to be extended if new -R exceeds existing boundaries.
34 Append nodata value to initialize nodes outside current region
35 [Default is NaN].
36 -Rxmin/xmax/ymin/ymax[+r][+uunit] (more ...)
38 Specify the region of interest. This defines the subregion to be
39 cut out.
40 -S[n]lon/lat/radius[unit]
42 Specify an origin and radius; append a distance unit (see UNITS)
43 and we determine the corresponding rectangular region so that
44 all grid nodes on or inside the circle are contained in the sub‐
45 set. If -Sn is used we set all nodes outside the circle to NaN.
46 -V[level] (more ...)
48 Select verbosity level [c].
49 -Z[n|r]min/max
51 Determine the new rectangular region so that all nodes outside
52 this region are also outside the given z-range [-inf/+inf]. To
53 indicate no limit on min or max, specify a hyphen (-). Normally,
54 any NaNs encountered are simply skipped and not considered in
55 the decision. Use -Zn to consider a NaN to be outside the
56 z-range. This means the new subset will be NaN-free. Alterna‐
57 tively, use -Zr to consider NaNs to be within the data range. In
58 this case we stop shrinking the boundaries once a NaN is found
59 [Default simply skips NaNs when making the range decision].
60 -f[i|o]colinfo (more ...)
62 Specify data types of input and/or output columns.
63 -^ or just -
65 Print a short message about the syntax of the command, then
66 exits (NOTE: on Windows just use -).
67 -+ or just +
69 Print an extensive usage (help) message, including the explana‐
70 tion of any module-specific option (but not the GMT common
71 options), then exits.
72 -? or no arguments
74 Print a complete usage (help) message, including the explanation
75 of all options, then exits.
76
78 For map distance unit, append unit d for arc degree, m for arc minute,
79 and s for arc second, or e for meter [Default], f for foot, k for km, M
80 for statute mile, n for nautical mile, and u for US survey foot. By
81 default we compute such distances using a spherical approximation with
82 great circles. Prepend - to a distance (or the unit is no distance is
83 given) to perform "Flat Earth" calculations (quicker but less accurate)
84 or prepend + to perform exact geodesic calculations (slower but more
85 accurate).
86
88 By default GMT writes out grid as single precision floats in a
89 COARDS-complaint netCDF file format. However, GMT is able to produce
90 grid files in many other commonly used grid file formats and also
91 facilitates so called "packing" of grids, writing out floating point
92 data as 1- or 2-byte integers. (more ...)
93
95 When the output grid type is netCDF, the coordinates will be labeled
96 "longitude", "latitude", or "time" based on the attributes of the input
97 data or grid (if any) or on the -f or -R options. For example, both
98 -f0x -f1t and -R90w/90e/0t/3t will result in a longitude/time grid.
99 When the x, y, or z coordinate is time, it will be stored in the grid
100 as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH
101 in the gmt.conf file or on the command line. In addition, the unit
102 attribute of the time variable will indicate both this unit and epoch.
103
105 Suppose you have used surface to grid ship gravity in the region
106 between 148E - 162E and 8N - 32N, and you do not trust the gridding
107 near the edges, so you want to keep only the area between 150E - 160E
108 and 10N - 30N, then:
109 gmt grdcut grav_148_162_8_32.nc -Ggrav_150_160_10_30.nc -R150/160/10/30 -V
111 To return the subregion of a grid such that any boundary strips where
113 all values are entirely above 0 are excluded, try
114 gmt grdcut bathy.nc -Gtrimmed_bathy.nc -Z-/0 -V
116 To return the subregion of a grid that contains all nodes within a dis‐
118 tance of 500 km from the point 45,30 try
119 gmt grdcut bathy.nc -Gsubset_bathy.nc -S45/30/500k -V
121
123 gmt, grdclip, grdinfo, grdpaste, surface
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126 2019, P. Wessel, W. H. F. Smith, R. Scharroo, J. Luis, and F. Wobbe
1275.4.5 Feb 24, 2019 GRDCUT(1)