Creating polygon from perpendicular projection of light on wall on DEM using GRASS
Geographic Information Systems Asked on May 21, 2021
Scenario:
I have
- a DEM
- a Polyline with elevation, representing a man made barrier like a levee or a giant wall.
Polyline will always be on top of DEM.
I want to get a polygon that represent all the areas that will be shaded if we were to project a perpendicular light along the wall.
Do we have tools in GRASS to achieve this?
Sketch:
I want the blue polygon.
One Answer
As @Vince pointed out, the GRASS module r.viewshed (man page) will achieve what you want. You'll need to first "burn" the wall into your DEM. Then set the coordinates= parameter to the location of the light, and use the -b parameter so that the output raster will have 1 or 0 for visible/invisible (i.e. lighted/dark).
Answered by Micha on May 21, 2021
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