1GRDCUT(1) Generic Mapping Tools GRDCUT(1)
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6 grdcut - Extract a subregion out of a grid file
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9 grdcut input_file.grd -Goutput_file.grd -Rwest/east/south/north[r] [ -V
10 ] [ -f[i|o]colinfo ]
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13 grdcut will produce a new output_file.grd file which is a subregion of
14 input_file.grd. The subregion is specified with -R as in other pro‐
15 grams; the specified range must not exceed the range of input_file.grd.
16 If in doubt, run grdinfo to check range. Complementary to grdcut there
17 is grdpaste, which will join together two grid files along a common
18 edge.
19 input_file.grd
21 this is the input .grd format file.
22 -Goutput_file.grd
24 this is the output .grd format file.
25 -R xmin, xmax, ymin, and ymax specify the Region of interest. For
27 geographic regions, these limits correspond to west, east,
28 south, and north and you may specify them in decimal degrees or
29 in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
30 and upper right map coordinates are given instead of w/e/s/n.
31 The two shorthands -Rg and -Rd stand for global domain (0/360
32 and -180/+180 in longitude respectively, with -90/+90 in lati‐
33 tude). For calendar time coordinates you may either give (a)
34 relative time (relative to the selected TIME_EPOCH and in the
35 selected TIME_UNIT; append t to -JX|x), or (b) absolute time of
36 the form [date]T[clock] (append T to -JX|x). At least one of
37 date and clock must be present; the T is always required. The
38 date string must be of the form [-]yyyy[-mm[-dd]] (Gregorian
39 calendar) or yyyy[-Www[-d]] (ISO week calendar), while the clock
40 string must be of the form hh:mm:ss[.xxx]. The use of delim‐
41 iters and their type and positions must be exactly as indicated
42 (however, input, output and plot formats are customizable; see
43 gmtdefaults). This defines the subregion to be cut out.
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46 -V Selects verbose mode, which will send progress reports to stderr
47 [Default runs "silently"].
48 -f Special formatting of input and/or output columns (time or geo‐
50 graphical data). Specify i or o to make this apply only to
51 input or output [Default applies to both]. Give one or more
52 columns (or column ranges) separated by commas. Append T (abso‐
53 lute calendar time), t (relative time in chosen TIME_UNIT since
54 TIME_EPOCH), x (longitude), y (latitude), or f (floating point)
55 to each column or column range item. Shorthand -f[i|o]g means
56 -f[i|o]0x,1y (geographic coordinates).
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59 By default GMT writes out grid as single precision floats in a COARDS-
60 complaint netCDF file format. However, GMT is able to produce grid
61 files in many other commonly used grid file formats and also facili‐
62 tates so called "packing" of grids, writing out floating point data as
63 2- or 4-byte integers. To specify the precision, scale and offset, the
64 user should add the suffix =id[/scale/offset[/nan]], where id is a two-
65 letter identifier of the grid type and precision, and scale and offset
66 are optional scale factor and offset to be applied to all grid values,
67 and nan is the value used to indicate missing data. When reading
68 grids, the format is generally automatically recognized. If not, the
69 same suffix can be added to input grid file names. See grdreformat(1)
70 and Section 4.17 of the GMT Technical Reference and Cookbook for more
71 information.
72 When reading a netCDF file that contains multiple grids, GMT will read,
74 by default, the first 2-dimensional grid that can find in that file. To
75 coax GMT into reading another multi-dimensional variable in the grid
76 file, append ?varname to the file name, where varname is the name of
77 the variable. Note that you may need to escape the special meaning of ?
78 in your shell program by putting a backslash in front of it, or by
79 placing the filename and suffix between quotes or double quotes. The
80 ?varname suffix can also be used for output grids to specify a variable
81 name different from the default: "z". See grdreformat(1) and Section
82 4.18 of the GMT Technical Reference and Cookbook for more information,
83 particularly on how to read splices of 3-, 4-, or 5-dimensional grids.
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86 When the output grid type is netCDF, the coordinates will be labeled
87 "longitude", "latitude", or "time" based on the attributes of the input
88 data or grid (if any) or on the -f or -R options. For example, both
89 -f0x -f1t and -R90w/90e/0t/3t will result in a longitude/time grid.
90 When the x, y, or z coordinate is time, it will be stored in the grid
91 as relative time since epoch as specified by TIME_UNIT and TIME_EPOCH
92 in the .gmtdefaults file or on the command line. In addition, the unit
93 attribute of the time variable will indicate both this unit and epoch.
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96 Suppose you have used surface to grid ship gravity in the region
97 between 148E - 162E and 8N - 32N, and you do not trust the gridding
98 near the edges, so you want to keep only the area between 150E - 160E
99 and 10N - 30N, then:
100 grdcut grav_148_162_8_32.grd -Ggrav_150_160_10_30.grd -R150/160/10/30
102 -V
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105 grdpaste(1), grdinfo(1), GMT(1)
106GMT 4.3.1 15 May 2008 GRDCUT(1)