[GRASS-user] Viewsheds

[Mark Lake]

Paul,

> Before I recommend to my boss that we use GRASS for
> this, I wanted to confirm that r.los does, in fact, account for the  
> Earth's
> curvature. Unfortunately, the online manpage makes no mention of  
> it, so I
> was wondering if anyone can tell me if it does or doesn't.

r.los does not correct for curvature of the earth.  The latest  
version of r.cva - upgraded by benjamin Ducke - does however have  
this option.  You can get it from my site <http://www.ucl.ac.uk/ 
~tcrnmar/> or Benjamin's site <http://www.uni-kiel.de/ufg/ 
ufg_BerDucke.htm>.

Although r.cva is designed for multiple and cumulative viewshed  
analysis, you can use it for calculating individual viewsheds if you  
create a vector map containing the single viewpoint.  Note also that  
whereas r.los returns a map containing the inclination at which  
target cells are visible, r.cva (when used to calculate one viewshed)  
will essentially just return a binary map (i.e. visible or not).  You  
will also need to invoke the -f flag (see the man page) to get the  
effect you want.

Mark


--
Dr Mark Lake

Institute of Archaeology
University College London
31-34 Gordon Square
London.  WC1H 0PY

Tel: +44 (0)207 679 7495
Fax: +44 (0)207 383 2572