6 replies to this topic

[Martin Gamache]

I'm looking for a way to create a cast shadow mask from a DEM given an light source azimuth and solar elevation?

[frax]

you have ArcGIS don't you? The hillshade command has the options both/shade/shadow - run it with only shadow and see what it looks like - isn't that what you are looking for?

[Martin Gamache]

Hugo,


I did just that, I had to go and find a place with a version of spatial analyst first. The shadow option worked great. The metadata file for my Landsat image had the elevation and azimuth value. The algorithm assigns a value of zero to all the shadows. All I had to do is reclassify the image and create a 2 bit mask and I was in business.

I was hoping to find a non spatial analyst way to do it from the comfort of my office but....

[frax]

well, if the machine with spatial analyst is networked, and has ArcInfo workstation installed, you should be able to do it through a console (telnet/ssh). But then maybe you could use something like VNC too, and use the GUI that way.

[Kartograph]

Hugo, I think Martin might not be legally allowed to do just that...

[Martin Gamache]

I have access through a couple of legit ways. Since this was part of a class assignment, I was able to use a school machine to generate the mask. I'm able to access some unix software through an X_win session from myoffice but ARC isnt one of them so I had to actually go there and physically do it. It got complicated because the first time I went the DEM data had somehow gotten corrupt on my USB key.... to make a long story short, it was a long day.

The ARC algorithm seems to slightly underestimate shadows, of course it is a function of the DEM accuracy....

[rmcculley]

I don't know how well this will work as I haven't tried it:

http://www.perrygeo.net/wordpress/?p=7

[Edit]Now that I've re-read that page, I see that it might not do what you are looking for.[/Edit]