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(1gmt), grdmath(1gmt), grdclip(1gmt), psmask(1gmt), psclip(1gmt), pscoast(1gmt)

                                                   1 Jan 2004                                     GRDLANDMASK(l)