Input maps may have NULL values. For example, if you have a raster mask set for a watershed (using basin map from r.water.outlet), the following command will create a masked elevation map (belev):
r.mapcalc "belev = if(isnull(basin), basin, elev)"
r.stats -Anc prints out averaged statistics for topographic index.
Lat/long projects are not supported. If data is not projected, please create a new project with a projected coordinate reference system and reproject the data there. Please run r.topidx from that project.
g.region raster=elevation -p r.topidx input=elevation output=topidx_elevation
Moore, I.D., R.B. Grayson, and A.R. Ladson, 1991. Digital Terrain Modeling: A Review of Hydrological, Geomorphological, and Biological Applications. Hydrological Processes 5:3-30.
Based on GRIDATB.FOR by Keith Beven.