grdclip - Clip the range of grid values
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.
- The input 2-D binary grid file.
- outgrid is the modified output grid file.
- -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 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.
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 ...)
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