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

[Josh Doe]

On Fri, Oct 7, 2011 at 2:28 AM, Markus Metz
<markus.metz.giswork at googlemail.com> wrote:
> On Fri, Oct 7, 2011 at 7:49 AM, Josh Doe <josh at joshdoe.com> wrote:
>> 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?
>>
> r.viewshed in the grass-addons can do exactly that what you want.

Indeed, it looks to fit the bill perfectly, thanks! The only trouble
now is getting it compiled. I'm on Windows XP, and it seems the
Makefile doesn't work out of the box. I also tried g.extension, but it
complains of SVN missing, though I'm not sure what svn client it needs
(I've got a Cygwin svn.exe, but adding my Cygwin bin to the path
doesn't seem to help matters).

Hopefully I'll get it working soon, thanks for the reference.

-Josh