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 ] [ -bo[s][n] ]


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/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 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 std-
       out if no output gridfile name is 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
              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.


OPTIONS

       -G     Name  of  output grid file. If not set, the grid will be written
              as ASCII (or binary; see -boxyz-triplets to stdout instead.

       -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 UNIT/degree, 1:xxxxx, or
              width in UNIT (upper case modifier).  UNIT is cm,  inch,  or  m,
              depending  on the MEASURE_UNIT setting in .gmtdefaults, but this
              can be overridden on the command line by appending the c, i,  or
              m to the scale/width value.

              CYLINDRICAL PROJECTIONS:

              -Jclon0/lat0/scale (Cassini)
              -Jjlon0/scale (Miller)
              -Jmscale (Mercator - Greenwich and Equator as origin)
              -Jmlon0/lat0/scale (Mercator - Give meridian and standard paral-
              lel)
              -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  Car-
              ree))
              -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/[slat/]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:

              -Jp[a]scale[/origin]  (polar  (theta,r)  coordinates, optional a
              for azimuths and offset theta [0])
              -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"].

       -bo    Selects binary output. Append s for single precision [Default is
              double].  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, 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

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

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



SEE ALSO

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


REFERENCES

       Wessel, P., and W. H. F. Smith, 2001, The Generic Mapping  Tools  (GMT)
       version 3.4 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.



                                  1 Jan 2004                      GRDRASTER(l)

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