grdclip man page

grdclip — Clip the range of grids


grdclip ingrid outgrid [ region ] [ ahigh/above ] [ blow/below ] [ ilow/high/between ] [ rold/new ] [ [level] ]

Note: No space is allowed between the option flag and the associated arguments.


grdclip will set values < low to below and/or values > high to above. You can also specify one or more intervals where all values should be set to IT(between), or replace individual values. Such operations are useful when you want all of a continent or an ocean to fall into one color or gray shade in image processing, when clipping of the range of data values is required, or for reclassification of data values. above, below, between, old and new can be any number or even NaN (Not a Number). You must choose at least one of the -S options. Use -R to only extract a subset of the ingrid file.

Required Arguments

The input 2-D binary grid file.
outgrid is the modified output grid file.

Optional Arguments

-R[unit]xmin/xmax/ymin/ymax[r] (more ...)
Specify the region of interest. Using the -R option will select a subsection of ingrid grid. If this subsection exceeds the boundaries of the grid, only the common region will be extracted.
Set all data[i] > high to above.
Set all data[i] < low to below.
Set all data[i] >= low and <= high to between. Repeat the option for as many intervals as are needed.
Set all data[i] == old to new. This is mostly useful when your data are known to be integer values. Repeat the option for as many replacements as are needed.
-V[level] (more ...)
Select verbosity level [c].
-^ or just -
Print a short message about the syntax of the command, then exits (NOTE: on Windows use just -).
-+ or just +
Print an extensive usage (help) message, including the explanation of any module-specific option (but not the GMT common options), then exits.
-? or no arguments
Print a complete usage (help) message, including the explanation of options, then exits.
Print GMT version and exit.
Print full path to GMT share directory and exit.

Grid File Formats

By default GMT writes out grid as single precision floats in a COARDS-complaint netCDF file format. However, GMT is able to produce grid files in many other commonly used grid file formats and also facilitates so called "packing" of grids, writing out floating point data as 1- or 2-byte integers. To specify the precision, scale and offset, the user should add the suffix =id[/scale/offset[/nan]], where id is a two-letter identifier of the grid type and precision, and scale and offset are optional scale factor and offset to be applied to all grid values, and nan is the value used to indicate missing data. In case the two characters id is not provided, as in =/scale than a id=nf is assumed. When reading grids, the format is generally automatically recognized. If not, the same suffix can be added to input grid file names. See grdconvert and Section grid-file-format of the GMT Technical Reference and Cookbook for more information.

When reading a netCDF file that contains multiple grids, GMT will read, by default, the first 2-dimensional grid that can find in that file. To coax GMT into reading another multi-dimensional variable in the grid file, append ?varname to the file name, where varname is the name of the variable. Note that you may need to escape the special meaning of ? in your shell program by putting a backslash in front of it, or by placing the filename and suffix between quotes or double quotes. The ?varname suffix can also be used for output grids to specify a variable name different from the default: "z". See grdconvert and Sections modifiers-for-CF and grid-file-format of the GMT Technical Reference and Cookbook for more information, particularly on how to read splices of 3-, 4-, or 5-dimensional grids.


To set all values > 70 to NaN and all values < 0 to 0 in file data.nc:

gmt grdclip data.nc -Gnew_data.nc -Sa70/NaN -Sb0/0 -V

To reclassify all values in the 25-30 range to 99, those in 35-39 to 55, exchange 17 for 11 and all values < 10 to 0 in file classes.nc, try

gmt grdclip classes.nc -Gnew_classes.nc -Si25/30/99 -Si35/39/55 -Sr17/11 -Sb10/0 -V

See Also

gmt, grdlandmask, grdmask, grdmath, grd2xyz, xyz2grd


GMT 5.2.1 November 12, 2015