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I have multiple raster files that overlap each other. I am using the r.cross GRASS tool to find all of the unique combinations of values from my inputs. The tool works properly, and I get a new raster file with arbitrary values representing all of the unique combinations. However, in the Help tab of the tool under Support Files, it states that a "category file created for the output raster map layer describes the combinations of input map layer category values which generated each category." Where do I find this file? It is very important to me to know which raster layers and what values within those layers contributed to the output from the r.cross tool. The output is supposed to look something like this:

      category   category
      value      label
      ______________________________
         1       layer1(0) layer2(1)
         2       layer1(0) layer2(2)
         3       layer1(1) layer2(1)
         4       layer1(1) layer2(2)
         5       layer1(2) layer2(4)

2 Answers 2

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Quite unfortunately (as of today; QGIS 2.18.19 and 3.0.2), GRASS in the QGIS Processing Toolbox does not have capability to return the summary.

A workaround is to run r.report command after the r.cross, to include all of:

  • Input raster files to r.cross
  • Output raster file from r.cross

as the input layer to r.report command.

The r.report will return all combination of these input layers as a summary table (Category Information)

enter image description here

The report is displayed by the Results viewer (under Processing pull-down menu).

Because we cannot select the order of input layers to r.report, the output table is commonly displayed in unfavorable manner. (Oh well, let's hope r.cross is fixed soon...)

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  • I did not have a nice set of raster files... the report (added image) shows (1) raster with all cell value is 27, (2) all cell value is set to 0, (3) copy of the layer (1). Not a good example, really.
    – Kazuhito
    May 1, 2018 at 19:40
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I recommend to use Semi-Automatic Classification Plugin plugin instead, in which you can use post-processing tool, there is one called "Land cover change". This options gives you both raster and table outputs

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