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


       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 ]


       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.


       -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

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

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


       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


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

                                            1 Jan 2004                             GRDLANDMASK(l)