grdlandmask (1gmt)

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 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"].

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)