grdclip − Clipping of range in grid files.
grdclip input_file.grd −Goutput_file.grd [ −Sahigh/above ] [ −Sblow/below ] [ −V ]
grdclip
will set values < low to below and/or
values > high to above. Useful when you
want all of a continent or an ocean to fall into one color
or grayshade in image processing, or clipping of the range
of data values is required. above/below can be any
number or NaN (Not a Number). You must choose at least one
of −Sa or −Sb.
input_file.grd
The input 2-D binary grid file.
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−G |
output_file.grd is the modified output grid file. |
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−Sa |
Set all data[i] > high to above. |
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−Sb |
Set all data[i] < low to below. |
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−V |
Selects verbose mode, which will send progress reports to stderr [Default runs "silently"]. |
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 2- or 4-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. When reading grids, the format is generally automatically recognized. If not, the same suffix can be added to input grid file names. See grdreformat(1) and Section 4.17 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 grdreformat(1) and Section 4.18 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.grd:
grdclip data.grd −G new_data.grd −Sa 70/NaN −Sb 0/0 −V
GMT(1), grdlandmask(1), grdmask(1), grdmath(1), grd2xyz(1), xyz2grd(1)