[GRASS-user] r.sun vs r.sunmask

Patrick S. patrick_GIS at gmx.ch
Fri Oct 19 08:50:14 PDT 2012

Dear List,

I am trying to create a hillshade map with shadowing effect of the 
topography. It seems r.sunmask should be my weapon of choice, but it is 
incredibly slow. Then I found a mail to the userlist in 2007 where 
Markus replies on this 
saying that extracting NULL values of the incidence angle map in r.sun 
would be an alternative.

Is this still the better way or are there alternatives nowadays? I might 
miss something as the tool is quite complex in its options and am not 
aware of how to use the r.horizon approach, but running r.sun in simple 
mode -using elevation, aspect and slope as input- is still slow and 
produces a gradient across the map. Am not sure if this is the correct 

r.sun -s elevin=r_dem incidout=r_sun_shadow aspin=r_aspect 
slopein=r_slope day=80 time=17 --o

Thank you for any help.


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