GRASS GIS manual: r.category.trim

NAME

r.category.trim - Export categories and corresponding colors as QGIS colour file or csv file. Non-existing categories and their colour definitions will be removed.

KEYWORDS

raster, color, color table, category

SYNOPSIS

r.category.trim

r.category.trim --help

r.category.trim [-n] input=name [output=name] [csv=name] [qgis=name] [--overwrite] [--help] [--verbose] [--quiet] [--ui]

Flags:

-n: Recode layer to get consecutive category values
--overwrite: Allow output files to overwrite existing files
--help: Print usage summary
--verbose: Verbose module output
--quiet: Quiet module output
--ui: Force launching GUI dialog

Parameters:

input=name [required]: input map
output=name: output map
csv=name: Attribute table (csv format)
qgis=name: QGIS color file (txt format)

DESCRIPTION
NOTE
Examples
See also
AUTHOR

DESCRIPTION

Trim redundant category labels and colors

In GRASS you can 'cut out' a subset of a larger raster layer by setting the extent to something smaller then the extent of the original map using g.region and/or by setting a mask using r.mask, after which you simply run r.mapcalc "newmap = oldmap".

You may have noticed that when creating the new map, all category category labels and colour table of the original map are copied over to the new map, even for category values that are not in the new map. If you are working with categorical maps, this may not be what you want. See here for a more detailed discussion.

With this addon you can trim the category and colour tables so it only contains category labels and colour definitions for the values present in the new map. You can do this on the input map, or do this on a copy of the map.

Recode to consecutive category values

If you prefer the map to have consecutive values (i.e., without gaps), there is the option to change the category values to a consecutive series by setting the n-flag. For example, if the map has the following categories values and labels (after the redundant category labels have been removed):

2 label2
5 label5
9 label9

Then the new recoded layer will have the category values and labels:

1 label2
2 label5
3 label9

Export QGIS color map file

The addon let's you export the categories, category labels and colours as QGIS colour map file. This is just a simple text file with the raster categories and corresponding colour definitions and category labels. QGIS can use this to set the colour and labels for a raster layer. See this blogpost for more details how to use the colour map file in QGIS. Alternatively, you can also export the categories and category labels as a normal comma separated calues (CSV) file file, which can be easily viewed in a spreadsheet program such as Libre/Open Office Calc, Microsoft Excel, or Google Docs and can be easily shared together with an exported raster file for users that use other GIS programs

NOTE

The file is only useful for categorical maps. Therefore only integer maps are accepted as input. To export color maps for continuous raster layers (or as an alternative to this plugin), have a look at the r.colors.out_sld plugin. To get QGIS color files, you need a two step approach: (1) create a sld file using the r.colors.out_sld plugin, and (2) in QGIS, use the SLD4raster plugin to convert this to a qml file.

When you use the option to recode the map, you need to set an output map as well. It uses the r.recode function, with the 'a' flag set, i.e., the region is aligned to the input raster map.

Examples

See here for examples

AUTHOR

Paulo van Breugel, paulo at ecodiv.earth

Last changed: $Date: 2017-03-15 14:08:20 +0100 (Wed, 15 Mar 2017) $

SOURCE CODE

Available at: r.category.trim source code (history)