[GRASS-user] Using r.los to find where an object could be hidden

[Josh Doe]

I've just used r.los for the first time, but want to do something
slightly different this time. Instead of finding what points
on-the-ground are visible by the observer, I want to find what points
at a height above-the-ground are visible by the observer. Or the
inverse, given a height of an object (person, tree, whatever), what
areas could hide these objects. I'm guessing I can't make r.los do
what I want without modifying the code.

Just to be clear, the results I'm looking for will indicate a spot is
visible even behind a hill, so long as the object height is
sufficiently large enough to appear above the top of the hill.

Does anyone know of a trick to do what I want, or perhaps have done
something similar and can share a script?

Thanks,
-Josh