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[/min_level/max_level] ] [
      -Dresolution ] [ -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 that is lower than min_level or 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 resolution drops off by
           ~80% between data sets. [Default is l].  Note that because the
           coastlines differ in details a node in a mask file using one
           resolution is not guaranteed to remain inside [or outside] when a
           different resolution is selected.

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

      -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 -N1/NaN -Gland_mask.grd -V

      To make a 1x1 degree global grid with the hierarchical levels 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