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 infor-
mation to decide which nodes in the specified grid are over land or
over water. The nodes defined by the selected region and lattice spac-
ing 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 opera-
tions 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 hier-
archical 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(l), grdmath(l), grdclip(l), psmask(l), psclip(l), pscoast(l)
GMT3.4.6 1 Jan 2005 GRDLANDMASK(l)
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