[GRASS-user] long run time with r.sunmask

[Dylan Beaudette]

On Thursday 08 March 2007 14:17, Hamish wrote:
> Markus Neteler wrote:
> > Dylan Beaudette wrote on 03/08/2007 02:25 AM:
> > > Hi everyone,
> > >
> > > using the latest CVS, I noticed that running r.sunmaks on a
> > > relatively small  region (300x300 cells) took a very long time to
> > > run (about 15 minutes). I am  using a DEM for the location and
> > > specifying the time of day, and day of the  year. I used the
> > > following command:
> > >
> > > r.sunmask elev=elev_meters out=shadows_afternoon timezone=-8
> > > year=2007 month=3  day=31 hour=16 minute=00 second=00
> > >
> > > Any idea on why this would take so long?
> >
> > ... because of r.sunmask slowliness...
> > For a fast solution, use r.sun instead.
> >   Shadow maps
> >        A  map  of  shadows can be extracted from the solar incidence
> > angle map (incidout). Areas with
> >        zero values are shadowed. The -s flag has to be used.

Thanks for the tips Markus. Fortunately this mini-analysis was not something I 
plan to do on a regular basis. However Hamish brings up a good point:

>
> any idea if this is because of the (better) SOLPOS algorithm r.sunmask
> uses, or is it just inefficient structure in the r.sunmask module?
>
> ie if/when r.sun is updated to use SOLPOS, can we expect a big slowdown
> in r.sun run times?
>
>

... as I make heavy use of r.sun and any issues related to either 

1. poor performance in SOLPOS
2. current inaccuracies in r.sun

are of interest to me. Could it be due to the on-the-fly computation of 
slope/aspect within SOLPOS?

Cheers,

-- 
Dylan Beaudette
Soils and Biogeochemistry Graduate Group
University of California at Davis
530.754.7341