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I have hypsometric model of relief, and I need to visualize shadows. I was suggested to use GRASS command r.sunmask, so I tried to set time values and run command, but it gives me an error

"ERROR: Neither sun position nor east/north, date/time/timezone definition are complete"

So then I tried to put values in Position tab, which I founded by SOLPOS Calculator (http://www.nrel.gov/midc/solpos/solpos.html)

r.sunmask elevation=model@PLANINA output=model_sunmask year=2011 month=1 day=15 hour=9 timezone=1 east=45.909361 north=15.965538

But it didn't work out, too, it says "Calculating shadows from DEM..." but nothing's going on for hours of waiting. So I ask if that command works at all in GRASS, or I'm doing something wrong?

You can suggest some other application for same thing, except ArcGIS applications. Thank you.

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Could you post the command you used? –  underdark May 10 '11 at 14:24
    
Do you need to visualize actual shadows or do you just need a shaded relief map? For the latter, look at r.shaded.relief –  whuber May 10 '11 at 14:32
    
r.sunmask elevation=model@PLANINA output=model_sunmask year=2011 month=1 day=15 hour=9 timezone=1 east=45.909361 north=15.965538 –  againstflow May 10 '11 at 14:35
    
I need to visualize actual shadows. –  againstflow May 10 '11 at 14:35
    
I haven't tried this, but I read that r.sun is faster and can be used by extracting 0 values from the incidout output. The 0 values are shadows. There is some debate about this here: osgeo-org.1803224.n2.nabble.com/… –  Paul May 10 '11 at 15:14

1 Answer 1

up vote 4 down vote accepted

Please use the r.sun command for this (-s for shadows). A map of shadows can be extracted from the solar incidence angle map ("incidout"): Areas with zero values are shadowed. Note that r.sunmask is terribly slow and r.sun the better choice.

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