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

[Patrick S.]

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 
issue(http://osgeo-org.1560.n6.nabble.com/long-run-time-with-r-sunmask-td3936587.html) 
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 
output.

Command:
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.


patrick