I am wondering if there is a way/tool in QGIS (2.6) could produce similar output as ArcGIS "Combine" tool does. I am trying to integrate values from overlapping rasters, and then create a single raster with unique value for each unique combination of input values. If there is a tool in QGIS could be used to get that will be the best. If not, should I using a script to automate reading through each pixel values? I am afraid it will take a large amount of time to processing national-wide data.
Here is the link to document for the "Combine" tool: http://desktop.arcgis.com/en/arcmap/10.3/tools/spatial-analyst-toolbox/combine.htm
Answer
Not tried it myself, but the GRASS algorithm r.stats will give total areas for each combination of cell values in multiple rasters. It seems to available (in 2.16 at least) via Processing.
The output isn't a raster though, it's a table, and it doesn't assign a new category number to each unique combination.
It will save you the trouble working out how to count how many cells have each combination, though. It also allows binning (e.g. aggregating over ranges of values like 0-9, 10-19, 20-29 etc.)
If it's an exact duplicate of the Arc functionality it would certainly be possible using Python and Numpy
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