I'm new to GRASS gis and I'm trying to do a topographic correction (i.topo.corr) of 9 ASTER bands using SRTM dem. I keep getting this error message:

ERROR: Illumination model is of CELL type

Is this error referring to my elevation raster, and if so how do I change the type to the appropriate one?

1 Answer 1


"CELL" type means integer type (see also http://grasswiki.osgeo.org/wiki/GRASS_raster_semantics#Raster_map_precision_types). Since SRTM is delivered as integer map but i.topo.corr expects a floating point map, you need to convert/resample that map beforehand.

For resampling methods available in GRASS GIS, see the manual or Wiki, especially:


since you may want to match the resolution of your DEM to that of the ASTER channels.

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