grdlandmask(1) [debian man page]
GRDLANDMASK(l) GRDLANDMASK(l) 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 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 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)
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GRDSAMPLE(l) GRDSAMPLE(l) NAME
grdsample - Resample a grd file onto a new grid SYNOPSIS
grdsample in_grdfile -Gout_grdfile [ -F ] [ -Idx[m|c][/dy[m|c]] ] [ -Lflag ] [ -Nnx/ny ] [ -Q ] [ -Rwest/east/south/north[r] ] [ -T ] [ -V ] DESCRIPTION
grdsample reads a grdfile and interpolates it to create a new grdfile with either: a different registration (-T); or, a new grid-spacing (-I) or number of nodes (-N), and perhaps also a new sub-region (-R). Interpolation is bicubic [Default] or bilinear (-Q) and uses boundary conditions (-L). Note that using (-R) only is equivalent to grdcut or grdedit -S. grdsample safely creates a fine mesh from a coarse one; the converse may suffer aliasing unless the data are filtered using grdfft or grdfilter. in_grdfile The name of the input 2-D binary grd file. -G The name of the output grd file. OPTIONS
No space between the option flag and the associated arguments. -F Force pixel registration. [Default is grid registration]. -I x_inc [and optionally y_inc] is the grid spacing. Append m to indicate minutes or c to indicate seconds. -L Boundary condition flag may be x or y or xy indicating data is periodic in range of x or y or both set by -R, or flag may be g indi- cating geographical conditions (x and y are lon and lat). [Default uses "natural" conditions (second partial derivative normal to edge is zero).] -N Specify number of columns nx and rows ny of new grid. -Q Quick mode, use bilinear rather than bicubic interpolation. -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. -T Translate between grid and pixel registration while keeping -R and -I the same; if input is grid-registered, output will be pixel- registered and vice-versa. The input file determines -R, -I and -N so no other options are necessary (except possibly -L or -Q). -V Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. HINTS
If an interpolation point is not on a node of the input grid, then a NaN at any node in the neighborhood surrounding the point will yield an interpolated NaN. Bicubic interpolation [default] yields continuous first derivatives but requires a neighborhood of 4 nodes by 4 nodes. Bilinear interpolation [-Q] uses only a 2 by 2 neighborhood, but yields only zeroth-order continuity. Use bicubic when smoothness is impor- tant. Use bilinear to minimize the propagation of NaNs. EXAMPLES
To resample the 5 x 5 minute grid in hawaii_5by5_topo.grd onto a 1 minute grid, try grdsample hawaii_5by5_topo.grd -I1m -Ghawaii_1by1_topo.grd To translate the gridline-registered file surface.grd to pixel registration, try grdsample surface.grd -T -Gpixel.grd SEE ALSO
gmt(1gmt), grdedit(1gmt), grdfft(1gmt), grdfilter(1gmt) 1 Jan 2004 GRDSAMPLE(l)