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

GRASS GRASS user
1

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

2

Patrick,

On Fri, Oct 19, 2012 at 5:50 PM, Patrick S. <patrick_GIS@gmx.ch> wrote:

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

I would leave the slope and aspect calculation to the module.
Be sure to set the computational region properly before running the
module:

# check if the resolution and extent are as desired, note that in
# mountainous areas the region must be larger to catch all
# shadows, use r.los or r.viewshed to get an idea about that:

g.region rast=r_dem -p

r.sun -s elevin=r_dem incidout=r_sun_shadow day=80 time=17

r.mapcalc "shadows = if (r_sun_shadow == 0, 1, null() )"

No idea about the gradient you reported, you need to tell us more about
your study area and its size.

Markus