I saw some posts by Markus about getting r.horizon and r.sun "synced" (such that the output files of r.horizon correspond to the time steps of r.sun)-- I was wondering if there are any conclusions on how best to use r.horizon and r.sun together so they most closely mimic using the -s shadow flag, specifically with daily integrations. We're about to start doing some MASSIVE r.sun processing (input DEM ~ 80gb) so we'd like to know how to pre-calculate the horizon info to speed this up. Thanks!
--j
--
Jonathan A. Greenberg, PhD
Postdoctoral Scholar
Center for Spatial Technologies and Remote Sensing (CSTARS)
University of California, Davis
One Shields Avenue
The Barn, Room 250N
Davis, CA 95616
Cell: 415-794-5043
AIM: jgrn307, MSN: jgrn307@hotmail.com, Gchat: jgrn307
On Fri, Nov 6, 2009 at 8:41 PM, Jonathan Greenberg
<greenberg@ucdavis.edu> wrote:
I saw some posts by Markus about getting r.horizon and r.sun "synced" (such
that the output files of r.horizon correspond to the time steps of r.sun)--
[ that was from Hamish ]
I was wondering if there are any conclusions on how best to use r.horizon
and r.sun together so they most closely mimic using the -s shadow flag,
specifically with daily integrations. We're about to start doing some
MASSIVE r.sun processing (input DEM ~ 80gb) so we'd like to know how to
pre-calculate the horizon info to speed this up. Thanks!
I have done such calculations last week. From all the tests done by Hamish
I got the conclusion that it is *currently* the best to not use r.horizon but
to calculate the horizon within r.sun.
Here what I used:
# step=0.05: 3 minutes time step alias 1deg sun movement
# horizonstep=1 to match step
Some notes (and multi-core parallelization trick) have been collected at http://grass.osgeo.org/wiki/R.sun
but a new section of "Recommendations" should be added there.
Contributions welcome.
> I was wondering if there are any conclusions on how best to use
> r.horizon and r.sun together so they most closely mimic using
> the -s shadow flag, specifically with daily integrations.
so if you use pre-calc'ed r.horizon maps you should not use the -s flag?
> We're about to start doing some MASSIVE r.sun processing (input
> DEM ~ 80gb)
how many cells? have you done trials with a subset of the data?
home much computer & time do you have to throw at the problem?
Markus:
# step=0.05: 3 minutes time step alias 1deg sun movement
# horizonstep=1 to match step
(fwiw I simplified a bit: actually 4 minute timestep is 1 deg (4*15=60),
but 3 min is a nice round step= so I used that as "better than 1deg")
Some notes (and multi-core parallelization trick) have been
collected at http://grass.osgeo.org/wiki/R.sun
but a new section of "Recommendations" should be added
there.
see also trac #498 linked from the above wiki page.