[GRASS5] searching for cast shadow algorithm (r.sunmask?)

GRASS GIS GRASS GIS developer
1

Hi again,

for my work I need a cast shadow algorithm. In GRASS 4.x
the r.sunmask did the job, I already tried to update it
to GRASS 5 (with help of Huidae). However, the CVS version
produces non-sense only.

Does anyone have such an algorithm available (calculate shadows
from given SUN position, local position and DEM)?

Thanks in advance

Markus

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2

Markus

you can try to run Jaro's r.sun with the -s flag, (read the manual page first,
whether it does what you need)
and you can see the animations for summer solstice day and winter solstice day
at the
end of the following document:
http://www2.gis.uiuc.edu:2280/modviz/viz/erosion.html
(it has nothing to do with erosion , it is about topo analysis).

Helena

Hi again,

for my work I need a cast shadow algorithm. In GRASS 4.x
the r.sunmask did the job, I already tried to update it
to GRASS 5 (with help of Huidae). However, the CVS version
produces non-sense only.

Does anyone have such an algorithm available (calculate shadows
from given SUN position, local position and DEM)?

Thanks in advance

Markus

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3

Hi Markus

Markus Neteler wrote:

Hi again,

for my work I need a cast shadow algorithm. In GRASS 4.x
the r.sunmask did the job, I already tried to update it
to GRASS 5 (with help of Huidae). However, the CVS version
produces non-sense only.

Does anyone have such an algorithm available (calculate shadows
from given SUN position, local position and DEM)?

For a shading algorithm you can check the following paper:

Fast Hill Shading with Specular Reflection and Cast Shadows - by C Ware
"Computers and Geosciences" 1989, 15, pages 1327-1334

I used an in-house library based on this algorithm for my Masters thesis
and it seemed to work well.

Hope this helps.

--
Sincerely,

Jazzman (a.k.a. Justin Hickey) e-mail: jhickey@hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand

People who think they know everything are very irritating to those
of us who do. ---Anonymous

Jazz and Trek Rule!!!

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4

Hi all,

many thanks for your recommendations on my shadow problem.

Good news: Huidae got the r.sunmask working (it's pretty slow
with FP maps, but working)!

You can test the current CVS version with a simple block in the landscape:

r.mapcalc test="if((row() > 100 && row() < 150 && col() > 100 && col() < 150),20,0)"
r.sunmask -z elev=test output=shadow alt=10 azim=45
d.rast shadow

Huidae, I have recoded the output values to:
no shadow: null()
shadow: 1

Is that o.k. with you?

On Mon, Mar 05, 2001 at 02:13:22PM +0700, Justin Hickey wrote:
[...]

For a shading algorithm you can check the following paper:

Fast Hill Shading with Specular Reflection and Cast Shadows - by C Ware
"Computers and Geosciences" 1989, 15, pages 1327-1334

I used an in-house library based on this algorithm for my Masters thesis
and it seemed to work well.

Other suggestions are the "-s" flag of r.sun or to modify a line of sight
algorithm.

Thanks for all your help,

Markus

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