grdmask - Create mask grdfiles from xy paths.
grdmask pathfiles -Gmask_grd_file] -Ixinc[m|c][/yinc[m|c]]
-Rwest/east/south/north[r] [ -A ] [ -F ] [ -H[nrec] ] [ -M[flag] ] [
-Nout/edge/in ] [ -S[radius][k] ] [ -V ] [ -: ] [ -bi[s][n] ] [
grdmask can operate in 2 different modes. 1. It reads one or more xy-
files that each define a closed polygon. The nodes defined by the
specified region and lattice spacing will be set equal to one of three
possible values depending on whether the node is outside, on the poly-
gon perimeter, or inside the polygon. The resulting mask grdfile may be
used in subsequent operations involving grdmath to mask out data from
polygonal areas. 2. The xy-files simply represent data point locations
and the mask is set to the inside or outside value depending on whether
a node is within a maximum distance from the nearest data point. If
the distance specified is zero then only the nodes nearest each data
point are considered "inside".
The name of 1 or more ASCII [or binary, see -b] files holding
the polygon(s) or data points.
-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 xmin, xmax, ymin, and ymax specify the Region of interest. For
geographic regions, these limits correspond to west, east,
south, and north and you may specify them in decimal degrees or
in [+-]dd:mm[:ss.xxx][W|E|S|N] format. Append r if lower left
and upper right map coordinates are given instead of wesn. The
two shorthands -Rg -Rd stand for global domain (0/360 or
-180/+180 in longitude respectively, with -90/+90 in latitude).
For calendar time coordinates you may either give relative time
(relative to the selected TIME_EPOCH and in the selected
TIME_UNIT; append t to -JX|x), or absolute time of the form
[date]T[clock] (append T to -JX|x). At least one of date and
clock must be present; the T is always required. The date string
must be of the form [-]yyyy[-mm[-dd]] (Gregorian calendar) or
yyyy[-Www[-d]] (ISO week calendar), while the clock string must
be of the form hh:mm:ss[.xxx]. The use of delimiters and their
type and positions must be as indicated (however, input/output
and plotting formats are flexible).
-A If the input data are geographic (as indicated by -fi) then the
sides in the polygons will be approximated by great circle arcs.
This can be turned off using the -A switch.
-F Force pixel registration. [Default is grid registration].
-H Input file(s) has Header record(s). Number of header records can
be changed by editing your .gmtdefaults4 file. If used, GMT
default is 1 header record. Use -Hi if only input data should
have header records [Default will write out header records if
the input data have them].
-M Multiple segment file. Segments are separated by a record whose
first character is flag. [Default is ’>’].
-N Sets the values that will be assigned to nodes that are outside
the polygons, on the edge, or inside. Values can be any number,
including the textstring NaN [Default is 0/0/1].
-S Set nodes depending on their distance from the nearest data
point. Nodes within radius  from a data point are considered
inside. Append k to indicate map units (e.g., -R and -I in
degrees and radius in km).
-V Selects verbose mode, which will send progress reports to stderr
[Default runs "silently"].
-bi Selects binary input. Append s for single precision [Default is
double]. Append n for the number of columns in the binary
[Default is 2 input columns].
-f Special formatting of input and output columns (time or geo-
graphical data) Specify i(nput) or o(utput) [Default is both
input and output]. Give one or more columns (or column ranges)
separated by commas. Append T (Absolute calendar time), t (time
relative to chosen TIME_EPOCH), x (longitude), y (latitude), g
(geographic coordinate), or f (floating point) to each column or
column range item.
To set all nodes inside and on the polygons coastline_*.xy to 0, and
outside points to 1, do
grdmask coastline_*.xy -R-60/-40/-40/-30 -I5m -N1/0/0 -Gland_mask.grd
To set nodes within 50 km of data points to 1 and other nodes to NaN,
grdmask data.xyz -R-60/-40/-40/-30 -I5m -NNaN/1/1 -S50k -Gdata_mask.grd
gmt(l), grdlandmask(l), grdmath(l), grdclip(l), psmask(l), psclip(l)
GMT4.0 1 Oct 2004 GRDMASK(l)
Man(1) output converted with