1GRDRASTER(1) Generic Mapping Tools GRDRASTER(1)
2
6 grdraster - extract subregion from a binary raster and write a grid
7 file
8
10 grdraster [ filenumber | "text pattern" ] -Rwest/east/south/north[r] [
11 -Ggrdfile ] [ -Ixinc[m|c][/yinc[m|c]] ] [ -Jparameters ] [ -V ] [
12 -bo[s|S|d|D[ncol]|c[var1/...]] ]
13
15 grdraster reads a file called grdraster.info from the current working
16 directory, the directories pointed to by the environment variables
17 $GMT_USERDIR and $GMT_GRIDDIR, or in $GMT_SHAREDIR/dbase (in that
18 order). The file grdraster.info defines binary arrays of data stored
19 in scan-line format in data files. Each file is given a filenumber in
20 the info file. grdraster figures out how to load the raster data into
21 a grid file spanning a region defined by -R. By default the grid spac‐
22 ing equals the raster spacing. The -I option may be used to sub-sample
23 the raster data. No filtering or interpolating is done, however; the
24 x_inc and y_inc of the grid must be multiples of the increments of the
25 raster file and grdraster simply takes every n'th point. The output of
26 grdraster is either grid or pixel registered depending on the registra‐
27 tion of the raster used. It is up to the GMT system person to maintain
28 the grdraster.info file in accordance with the available rasters at
29 each site. Raster data sets are not supplied with GMT but can be
30 obtained by anonymous ftp and on CD-ROM (see README page in dbase
31 directory). grdraster will list the available files if no arguments
32 are given. Finally, grdraster will write xyz-triplets to stdout if no
33 output gridfile name is given
34 filenumber
36 If an integer matching one of the files listed in the
37 grdraster.info file is given we will use that data set, else we
38 will match the given text pattern with the data set description
39 in order to determine the data set.
40 -R west, east, south, and north specify the Region of interest, and
43 you may specify them in decimal degrees or in
44 [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
45 upper right map coordinates are given instead of w/e/s/n. The
46 two shorthands -Rg and -Rd stand for global domain (0/360 and
47 -180/+180 in longitude respectively, with -90/+90 in latitude).
48 If r is appended, you may also specify a map projection to
49 define the shape of your region. The output region will be
50 rounded off to the nearest whole grid-step in both dimensions.
51
53 -G Name of output grid file. If not set, the grid will be written
54 as ASCII (or binary; see -bo xyz-triplets to stdout instead.
55 -I x_inc [and optionally y_inc] is the grid spacing. Optionally,
57 append a suffix modifier. Geographical (degrees) coordinates:
58 Append m to indicate arc minutes or c to indicate arc seconds.
59 If one of the units e, k, i, or n is appended instead, the
60 increment is assumed to be given in meter, km, miles, or nauti‐
61 cal miles, respectively, and will be converted to the equivalent
62 degrees longitude at the middle latitude of the region (the con‐
63 version depends on ELLIPSOID). If /y_inc is given but set to 0
64 it will be reset equal to x_inc; otherwise it will be converted
65 to degrees latitude. All coordinates: If = is appended then the
66 corresponding max x (east) or y (north) may be slightly adjusted
67 to fit exactly the given increment [by default the increment may
68 be adjusted slightly to fit the given domain]. Finally, instead
69 of giving an increment you may specify the number of nodes
70 desired by appending + to the supplied integer argument; the
71 increment is then recalculated from the number of nodes and the
72 domain. The resulting increment value depends on whether you
73 have selected a gridline-registered or pixel-registered grid;
74 see Appendix B for details.
75 -J Selects the map projection. Scale is UNIT/degree, 1:xxxxx, or
77 width in UNIT (upper case modifier). UNIT is cm, inch, or m,
78 depending on the MEASURE_UNIT setting in .gmtdefaults4, but this
79 can be overridden on the command line by appending c, i, or m to
80 the scale/width value. When central meridian is optional,
81 default is center of longitude range on -R option. Default
82 standard parallel is the equator. For map height, max dimen‐
83 sion, or min dimension, append h, +, or - to the width, respec‐
84 tively.
85 More details can be found in the psbasemap man pages.
86 CYLINDRICAL PROJECTIONS:
88 -Jclon0/lat0/scale (Cassini)
90 -Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
91 -Jj[lon0/]scale (Miller)
92 -Jm[lon0/[lat0/]]scale (Mercator)
93 -Jmlon0/lat0/scale (Mercator - Give meridian and standard paral‐
94 lel)
95 -Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and
96 azimuth)
97 -Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
98 -Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and
99 pole)
100 -Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
101 -Jtlon0/[lat0/]scale (TM - Transverse Mercator)
102 -Juzone/scale (UTM - Universal Transverse Mercator)
103 -Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)
104 CONIC PROJECTIONS:
106 -Jblon0/lat0/lat1/lat2/scale (Albers)
108 -Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
109 -Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
110 AZIMUTHAL PROJECTIONS:
112 -Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
114 -Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
115 -Jflon0/lat0[/horizon]/scale (Gnomonic)
116 -Jglon0/lat0[/horizon]/scale (Orthographic)
117 -Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale
118 (General Perspective).
119 -Jslon0/lat0[/horizon][/slat]/scale (General Stereographic)
120 MISCELLANEOUS PROJECTIONS:
122 -Jh[lon0/]scale (Hammer)
124 -Ji[lon0/]scale (Sinusoidal)
125 -Jkf[lon0/]scale (Eckert IV)
126 -Jk[s][lon0/]scale (Eckert IV)
127 -Jn[lon0/]scale (Robinson)
128 -Jr[lon0/]scale (Winkel Tripel)
129 -Jv[lon0/]scale (Van der Grinten)
130 -Jw[lon0/]scale (Mollweide)
131 NON-GEOGRAPHICAL PROJECTIONS:
133 -Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
135 -Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log,
136 and power scaling)
137 -V Selects verbose mode, which will send progress reports to stderr
139 [Default runs "silently"].
140 -bo Selects binary output. Append s for single precision [Default
142 is d (double)]. Uppercase S or D will force byte-swapping.
143 Optionally, append ncol, the number of desired columns in your
144 binary output file. This option applies only if no -G option
145 has been set.
146
148 To extract data from raster 1, taking one point every 30 minutes, in an
149 area extended beyond 360 degrees to allow later filtering, run
150 grdraster 1 -R-4/364/-62/62 -I30m -Gdata.grd
152 To obtain data for an oblique Mercator projection we need to extract
154 more data that is actually used. This is necessary because the output
155 of grdraster has edges defined by parallels and meridians, while the
156 oblique map in general does not. Hence, to get all the data from the
157 ETOPO2 data needed to make a contour map for the region defined by its
158 lower left and upper right corners and the desired projection, use
159 grdraster ETOPO2 -R160/20/220/30r -Joc190/25.5/292/69/1 -Gdata.grd
161 To extract data from the 2 min Geoware relief blend and write it as
163 binary double precision xyz-triplets to standard output:
164 grdraster "2 min Geoware" -R20/25/-10/5 -bo >! triplets.b
166
169 gmtdefaults(1), GMT(1), grdsample(1), grdfilter(1)
170
172 Wessel, P., and W. H. F. Smith, 2005, The Generic Mapping Tools (GMT)
173 version 4.1 Technical Reference & Cookbook, SOEST/NOAA.
174 Wessel, P., and W. H. F. Smith, 1998, New, Improved Version of Generic
175 Mapping Tools Released, EOS Trans., AGU, 79 (47), p. 579.
176 Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Map‐
177 ping Tools Released, EOS Trans., AGU, 76 (33), p. 329.
178 Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Map‐
179 ping Tools Released, http://www.agu.org/eos_elec/95154e.html, Copyright
180 1995 by the American Geophysical Union.
181 Wessel, P., and W. H. F. Smith, 1991, Free Software Helps Map and Dis‐
182 play Data, EOS Trans., AGU, 72 (41), p. 441.
183GMT 4.3.1 15 May 2008 GRDRASTER(1)