grdraster - extract subregion from a binary raster and write a grd file


       grdraster [ filenumber ] -Rwest/east/south/north[r] [ -Ggrdfilename ] [
       -Ix_inc[m|c][/y_inc[m|c]] ] [ -Jparams ] [ -V ] [ -bo[s] ]


       grdraster reads a file called from the directory pointed
       to by the environment parameter $GMT_GRIDDIR (if this parameter is  not
       set  it defaults to $GMTHOME/share/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 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 std-
       out if no output gridfile name is given

              An  integer  matching  one  of   the   files   listed   in   the

       -R     xmin,  xmax,  ymin, and ymax specify the Region of interest. For
              geographic regions,  these  limits  correspond  to  west,  east,
              south,  and north and you may specify them in decimal degrees or
              in [+-]dd:mm[][W|E|S|N] format. Append r  if  lower  left
              and  upper  right map coordinates are given instead of wesn. The
              two shorthands  -Rg  -Rd  stand  for  global  domain  (0/360  or
              -180/+180  in longitude respectively, with -90/+90 in latitude).
              For calendar time coordinates you may either give relative  time
              (relative  to  the  selected  TIME_EPOCH  and  in  the  selected
              TIME_UNIT; append t to -JX|x), or  absolute  time  of  the  form
              [date]T[clock]  (append  T  to  -JX|x). At least one of date and
              clock must be present; the T is always required. The date string
              must  be  of  the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
              yyyy[-Www[-d]] (ISO week calendar), while the clock string  must
              be  of  the form hh:mm:ss[.xxx]. The use of delimiters and their
              type and positions must be as indicated  (however,  input/output
              and  plotting  formats are flexible).  If r is appended, you may
              also specify a map  projection  to  define  the  shape  of  your
              region.  The  output  region  will be rounded off to the nearest
              whole grid-step in both dimensions.


       -G     Name of output grid file. If not set, the grid will  be  written


              -Jclon0/lat0/scale (Cassini)
              -Jjlon0/scale (Miller)
              -Jmscale (Mercator - Greenwich and Equator as origin)
              -Jmlon0/lat0/scale (Mercator - Give meridian and standard paral-
              -Joalon0/lat0/azimuth/scale  (Oblique  Mercator  -   point   and
              -Joblon0/lat0/lon1/lat1/scale (Oblique Mercator - two points)
              -Joclon0/lat0/lonp/latp/scale  (Oblique  Mercator  -  point  and
              -Jqlon0/scale (Equidistant Cylindrical  Projection  (Plate  Car-
              -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)


              -Jalon0/lat0/scale (Lambert).
              -Jelon0/lat0/scale (Equidistant).
              -Jflon0/lat0/horizon/scale (Gnomonic).
              -Jglon0/lat0/scale (Orthographic).
              -Jslon0/lat0/[slat/]scale (General Stereographic)

              CONIC PROJECTIONS:

              -Jblon0/lat0/lat1/lat2/scale (Albers)
              -Jdlon0/lat0/lat1/lat2/scale (Equidistant)
              -Jllon0/lat0/lat1/lat2/scale (Lambert)


              -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)


              -Jp[a]scale[/origin]  (polar  (theta,r)  coordinates, optional a
              for azimuths and offset theta [0])
              -Jxx-scale[l|ppow][/y-scale[l|ppow]][d] (Linear, log, and  power
              More details can be found in the psbasemap man pages.

       -V     Selects verbose mode, which will send progress reports to stderr
              [Default runs "silently"].

       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, use

       grdraster 3 -R160/20/220/30r -Joc190/25.5/292/69/1 -Gdata.grd

       To extract data from raster 3 and write it as binary  double  precision
       xyz-triplets to standard output:

       grdraster 3 -R20/25/-10/5 -bo >! triplets.b


       gmtdefaults(GMTMANSECTION),   gmt(GMTMANSECTION),  grdsample(GMTMANSEC-
       TION), grdfilter(GMTMANSECTION)


       Wessel, P., and W. H. F. Smith, 2004, The Generic Mapping  Tools  (GMT)
       version 4 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: 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.

GMT4.0                            1 Oct 2004          GRDRASTER(GMTMANSECTION)

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