NAME

     grdlandmask - Create "wet-dry" mask grdfile  from  shoreline
     data base.

SYNOPSIS

     grdlandmask  - Gmask_grd_file]  - Ixinc[m|c][/yinc[m|c]]   -
     Rwest/east/south/north[r] [ -Amin_area/max_level ] [ -Dreso-
     lution ] [ -F ] [ -Nmaskvalues[o] ] [ -V ]

DESCRIPTION

     grdlandmask reads the selected shoreline database  and  uses
     that information to decide which nodes in the specified grid
     are over land or over  water.   The  nodes  defined  by  the
     selected region and lattice spacing will be set according to
     one of two criteria:  (1) Lands vs water, or  (2)  the  more
     detailed  (hierarchial)  ocean  vs land vs lake vs island vs
     pond.  The resulting mask grdfile may be used in  subsequent
     operations  involving grdmath to mask out data from land [or
     water] areas.

     -G    Name of resulting output mask grd file.

     -I    x_inc [and optionally  y_inc]  is  the  grid  spacing.
          Append m to indicate minutes or c to indicate seconds.

     -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.

OPTIONS

     -A    Features with an area smaller than min_area in km^2 or
          of  hierarchical  level  higher  than max_level will be
          ignored [Default is 0/4 (all features)].  See  DATABASE
          INFORMATION in the pscoast man-pages for more details.

     -D    Selects the resolution of the data set to use ((f)ull,
          (h)igh,  (i)ntermediate, (l)ow, or (c)rude).  The reso-
          lution drops off by ~80% between data sets. [Default is
          l].

     -F    Force pixel registration.  [Default is grid  registra-
          tion].

     -N    Sets the  values  that  will  be  assigned  to  nodes.
          Values can be any number, including the textstring NaN.
          Append o to let nodes exactly on feature boundaries  be
          considered  outside  [Default is inside].  Specify this
          information using 1 of 2 formats:
               -Nwet/dry.
               -Nocean/land/lake/island/pond.

          [Default is 0/1/0/1/0 (i.e., 0/1)].

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

EXAMPLES

     To set all nodes on land to NaN, and nodes over water to  1,
     using the high resolution data set, do

     grdlandmask  - R-60/-40/-40/-30  - Dh   - I5m  -  NNaN/1   -
     Gland_mask.grd -V

     To make a 1x1 degree global grid with the hierarchical  lev-
     els of the nodes based on the low resolution data, try

     grdlandmask -R0/360/-90/90 -Dl  -I1 -N0/1/2/3/4 -Glevels.grd
     -V

SEE ALSO

     gmt, grdmath, grdclip, psmask, psclip, pscoast

REFERENCES

     Wessel, P., and W. H. F. Smith, 1995,  The  Generic  Mapping
     Tools  (GMT)  version  3.0  Technical  Reference & Cookbook,
     SOEST/NOAA.
     Wessel, P., and W. H. F. Smith, 1995,  New  Version  of  the
     Generic Mapping Tools Released, EOS Trans. AGU, 76, 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, p. 441.