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I'm starting to mess about with the solar radiation packages of GRASS and ArcGIS and have become rather stuck on the GRASS side of matters. I have a DSM area, and that is feeding into GRASS well enough, however when processing on the default values it falls over, not outputting anything. I'm using the command...

g.region rast=elevation.dem
r.sun -s elev=elevation.dem day=180
r.colors col=grey
d.his i_map=beam_map h_map=elevation.dem

In the R.Sun man page, the following command is recommended:

g.region rast=elevation.dem
r.sun -s elev=elevation.dem slop=slope asp=aspect beam=beam_map day=180
r.colors beam_map col=grey
d.his i_map=beam_map h_map=elevation.dem

However here, where am I supposed to get the slope, aspect and beam from?

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'Beam' is output. 'Slope' and 'Aspect' should be computed from the DEM. For details, follow the link at the bottom of the R.sun man page to the R.Slope.Aspect man page.

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