GRDRASTER(1) Generic Mapping Tools GRDRASTER(1)NAMEgrdraster - extract subregion from a binary raster and write a grid
file
SYNOPSISgrdraster [ filenumber | "text pattern" ] -Rwest/east/south/north[r] [
-Ggrdfile ] [ -Ixinc[m|c][/yinc[m|c]] ] [ -Jparameters ] [ -V ] [
-bo[s|S|d|D[ncol]|c[var1/...]] ]
DESCRIPTIONgrdraster reads a file called grdraster.info from the current working
directory, the directories pointed to by the environment variables
$GMT_DATADIR and $GMT_USERDIR, or in $GMT_SHAREDIR/dbase (in that
order). The file grdraster.info defines binary arrays of data stored
in scan-line format in data files. Each file is given a filenumber in
the info file. grdraster figures out how to load the raster data into
a grid file spanning a region defined by -R. By default the grid spac‐
ing equals the raster spacing. The -I option may be used to sub-sample
the raster data. No filtering or interpolating is done, however; the
x_inc and y_inc of the grid must be multiples of the increments of the
raster file and grdraster simply takes every n'th point. The output of
grdraster is either grid or pixel registered depending on the registra‐
tion of the raster used. It is up to the GMT system person to maintain
the grdraster.info file in accordance with the available rasters at
each site. Raster data sets are not supplied with GMT but can be
obtained by anonymous ftp and on CD-ROM (see README page in dbase
directory). grdraster will list the available files if no arguments
are given. Finally, grdraster will write xyz-triplets to stdout if no
output gridfile name is given
filenumber
If an integer matching one of the files listed in the
grdraster.info file is given we will use that data set, else we
will match the given text pattern with the data set description
in order to determine the data set.
-R west, east, south, and north specify the Region of interest, and
you may specify them in decimal degrees or in
[+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left and
upper right map coordinates are given instead of w/e/s/n. The
two shorthands -Rg and -Rd stand for global domain (0/360 and
-180/+180 in longitude respectively, with -90/+90 in latitude).
Alternatively, specify the name of an existing grid file and the
-R settings (and grid spacing, if applicable) are copied from
the grid. If r is appended, you may also specify a map projec‐
tion to define the shape of your region. The output region will
be rounded off to the nearest whole grid-step in both dimen‐
sions.
OPTIONS-G Name of output grid file. If not set, the grid will be written
as ASCII (or binary; see -bo xyz-triplets to stdout instead.
-I x_inc [and optionally y_inc] is the grid spacing. Optionally,
append a suffix modifier. Geographical (degrees) coordinates:
Append m to indicate arc minutes or c to indicate arc seconds.
If one of the units e, k, i, or n is appended instead, the
increment is assumed to be given in meter, km, miles, or nauti‐
cal miles, respectively, and will be converted to the equivalent
degrees longitude at the middle latitude of the region (the con‐
version depends on ELLIPSOID). If /y_inc is given but set to 0
it will be reset equal to x_inc; otherwise it will be converted
to degrees latitude. All coordinates: If = is appended then the
corresponding max x (east) or y (north) may be slightly adjusted
to fit exactly the given increment [by default the increment may
be adjusted slightly to fit the given domain]. Finally, instead
of giving an increment you may specify the number of nodes
desired by appending + to the supplied integer argument; the
increment is then recalculated from the number of nodes and the
domain. The resulting increment value depends on whether you
have selected a gridline-registered or pixel-registered grid;
see Appendix B for details. Note: if -Rgrdfile is used then
grid spacing has already been initialized; use -I to override
the values.
-J Selects the map projection. Scale is UNIT/degree, 1:xxxxx, or
width in UNIT (upper case modifier). UNIT is cm, inch, or m,
depending on the MEASURE_UNIT setting in .gmtdefaults4, but this
can be overridden on the command line by appending c, i, or m to
the scale/width value. When central meridian is optional,
default is center of longitude range on -R option. Default
standard parallel is the equator. For map height, max dimen‐
sion, or min dimension, append h, +, or - to the width, respec‐
tively.
More details can be found in the psbasemap man pages.
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jcyl_stere/[lon0/[lat0/]]scale (Cylindrical Stereographic)
-Jj[lon0/]scale (Miller)
-Jm[lon0/[lat0/]]scale (Mercator)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard paral‐
lel)
-Jo[a]lon0/lat0/azimuth/scale (Oblique Mercator - point and
azimuth)
-Jo[b]lon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and
pole)
-Jq[lon0/[lat0/]]scale (Cylindrical Equidistant)
-Jtlon0/[lat0/]scale (TM - Transverse Mercator)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jy[lon0/[lat0/]]scale (Cylindrical Equal-Area)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Conic Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert Conic Conformal)
-Jpoly/[lon0/[lat0/]]scale ((American) Polyconic)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0[/horizon]/scale (Lambert Azimuthal Equal-Area)
-Jelon0/lat0[/horizon]/scale (Azimuthal Equidistant)
-Jflon0/lat0[/horizon]/scale (Gnomonic)
-Jglon0/lat0[/horizon]/scale (Orthographic)
-Jglon0/lat0/altitude/azimuth/tilt/twist/Width/Height/scale
(General Perspective).
-Jslon0/lat0[/horizon]/scale (General Stereographic)
MISCELLANEOUS PROJECTIONS:
-Jh[lon0/]scale (Hammer)
-Ji[lon0/]scale (Sinusoidal)
-Jkf[lon0/]scale (Eckert IV)
-Jk[s][lon0/]scale (Eckert VI)
-Jn[lon0/]scale (Robinson)
-Jr[lon0/]scale (Winkel Tripel)
-Jv[lon0/]scale (Van der Grinten)
-Jw[lon0/]scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jp[a]scale[/origin][r|z] (Polar coordinates (theta,r))
-Jxx-scale[d|l|ppow|t|T][/y-scale[d|l|ppow|t|T]] (Linear, log,
and power scaling)
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-bo Selects binary output. Append s for single precision [Default
is d (double)]. Uppercase S or D will force byte-swapping.
Optionally, append ncol, the number of desired columns in your
binary output file. This option applies only if no -G option
has been set.
EXAMPLES
To extract data from raster 1, taking one point every 30 minutes, in an
area extended beyond 360 degrees to allow later filtering, run
grdraster 1 -R-4/364/-62/62 -I 30m -G data.grd
To obtain data for an oblique Mercator projection we need to extract
more data that is actually used. This is necessary because the output
of grdraster has edges defined by parallels and meridians, while the
oblique map in general does not. Hence, to get all the data from the
ETOPO2 data needed to make a contour map for the region defined by its
lower left and upper right corners and the desired projection, use
grdraster ETOPO2 -R 160/20/220/30r -Joc 190/25.5/292/69/1 -G data.grd
To extract data from the 2 min Geoware relief blend and write it as
binary double precision xyz-triplets to standard output:
grdraster "2 min Geoware" -R 20/25/-10/5 -bo >! triplets.b
SEE ALSOgmtdefaults(1), GMT(1), grdsample(1), grdfilter(1)REFERENCES
Wessel, P., and W. H. F. Smith, 2015, The Generic Mapping Tools (GMT)
version 4.5.14 Technical Reference & Cookbook, SOEST/NOAA.
Wessel, P., and W. H. F. Smith, 1998, New, Improved Version of Generic
Mapping Tools Released, EOS Trans., AGU, 79 (47), p. 579.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Map‐
ping Tools Released, EOS Trans., AGU, 76 (33), p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic Map‐
ping Tools Released, http://www.agu.org/eos_elec/95154e.html, Copyright
1995 by the American Geophysical Union.
Wessel, P., and W. H. F. Smith, 1991, Free Software Helps Map and Dis‐
play Data, EOS Trans., AGU, 72 (41), p. 441.
GMT 4.5.14 1 Nov 2015 GRDRASTER(1)
