NAME
grdraster - extract subregion from a binary raster and write a grd
file
SYNOPSIS
grdraster [ filenumber ] -Rwest/east/south/north[r] -Ggrdfilename [
-Ix_inc[m|c][/y_inc[m|c]] ] [ -Jparams ] [ -V ]
DESCRIPTION
grdraster reads a file called grdraster.info from the directory
pointed to by the environment parameter $GMT_GRIDDIR (if this
parameter is not set it defaults to $GMTHOME/lib/dbase). The info
file 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 grd file spanning a
region defined by -R. By default the grid spacing 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 grd file 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 registration 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.
filenumber
An integer matching one of the files listed in the grdraster.info
file.
-R west, east, south, and north specify the Region of interest. To
specify boundaries in degrees and minutes [and seconds], use the
dd:mm[:ss] format. Append r if lower left and upper right map
coordinates are given instead of wesn. If r is appended, you
must also specify a map projection to define the shape of your
region.
OPTIONS
-I x_inc [and optionally y_inc] is the grid spacing. Append m to
indicate minutes or c to indicate seconds.
-J Selects the map projection. Scale is inch/degree, 1:xxxxx, or
width in inch (upper case modifier).
CYLINDRICAL PROJECTIONS:
-Jclon0/lat0/scale (Cassini)
-Jjlon0/scale (Miller)
-Jmscale (Mercator - Greenwich and Equator as origin)
-Jmlon0/lat0/scale (Mercator - Give meridian and standard
parallel)
-Joalon0/lat0/azimuth/scale (Oblique Mercator - point and
azimuth)
-Joblon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
-Joclon0/lat0/lonp/latp/scale (Oblique Mercator - point and pole)
-Jqlon0/scale (Equidistant Cylindrical Projection (Plate Carree))
-Jtlon0/scale (TM - Transverse Mercator, with Equator as y = 0)
-Jtlon0/lat0/scale (TM - Transverse Mercator, set origin)
-Juzone/scale (UTM - Universal Transverse Mercator)
-Jylon0/lats/scale (Basic Cylindrical Projection)
AZIMUTHAL PROJECTIONS:
-Jalon0/lat0/scale (Lambert).
-Jelon0/lat0/scale (Equidistant).
-Jflon0/lat0/horizon/scale (Gnomonic).
-Jglon0/lat0/scale (Orthographic).
-Jslon0/lat0/scale (General Stereographic)
CONIC PROJECTIONS:
-Jblon0/lat0/lat1/lat2/scale (Albers)
-Jdlon0/lat0/lat1/lat2/scale (Equidistant)
-Jllon0/lat0/lat1/lat2/scale (Lambert)
MISCELLANEOUS PROJECTIONS:
-Jhlon0/scale (Hammer)
-Jilon0/scale (Sinusoidal)
-Jk[f|s]lon0/scale (Eckert IV (f) and VI (s))
-Jnlon0/scale (Robinson)
-Jrlon0/scale (Winkel Tripel)
-Jvlon0/scale (Van der Grinten)
-Jwlon0/scale (Mollweide)
NON-GEOGRAPHICAL PROJECTIONS:
-Jpscale (Linear projection for polar (theta,r) coordinates)
-Jxx-scale[l|ppow][/y-scale[l|ppow]] (Linear, log, and power
scaling)
More details can be found in the psbasemap manpages.
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
EXAMPLES
To extract data from raster 1, taking one point every 30 minutes, in
an area extended beyond 360 degrees to allow later filtering, try
grdraster 1 -R-4/364/-62/62 -I30m -Gdata.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 data
set 3 needed to make a contour map for the region defined by its lower
left and upper right corners and the desired projection, try
grdraster 3 -R160/20/220/30r -Joc190/25.5/292/69/1 -Gdata.grd
SEE ALSO
gmtdefaults, gmt, grdsample, grdfilter
REFERENCES
Wessel, P., and W. H. F. Smith, 1999, The Generic Mapping Tools (GMT)
version 3.2 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
Mapping Tools Released, EOS Trans., AGU, 76 (33), p. 329.
Wessel, P., and W. H. F. Smith, 1995, New Version of the Generic
Mapping 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
Display Data, EOS Trans., AGU, 72 (41), p. 441.
Man(1) output converted with
man2html