grdclip

Clip the range of grid values

Synopsis

gmt grdclip ingrid -Goutgrid [ -Rregion ] [ -Sahigh/above ] [ -Sblow/below ] [ -Silow/high/between ] [ -Srold/new ] [ -V[level] ] [ --PAR=value ]

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

Description

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 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

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

Optional Arguments

-Rxmin/xmax/ymin/ymax[+r][+uunit] (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.
-Sahigh/above
Set all data[i] > high to above.
-Sblow/below
Set all data[i] < low to below.
-Silow/high/between
Set all data[i] >= low and <= high to between. Repeat the option for as many intervals as are needed.
-Srold/new
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 just use -).
-+ 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 all options, then exits.
--PAR=value
Temporarily override a GMT default setting; repeatable. See gmt.conf for parameters.

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. (more …)

Examples

Note: Below are some examples of valid syntax for this module. The examples that use remote files (file names starting with @) can be cut and pasted into your terminal for testing. Other commands requiring input files are just dummy examples of the types of uses that are common but cannot be run verbatim as written.

To set all values > 0 to NaN and all values < 0 to 0 in the remote file AFR.nc:

gmt grdclip @AFR.nc -Gnew_AFR.nc -Sa0/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