- Re: r.los, or looking for other line of sight analysis

[Tom Poindexter]

On Tue, Jan 18, 2000 at 05:38:50PM +1030, Conn Copas wrote:
> Tom
> 
> Some things to check with r.los:
> 
> 1. Use g.region to ensure that your current region extent corresponds with that 
> of your elevation map. You can also coarsen up the resolution initially to make 
> things run faster whilst you are tweaking parameters.
> 
> 2. The "max_dist" parameter is fairly crucial, although it doesn't sound like 
> that is your problem.
> 
> 3. As a last resort, make sure that the version of Grass which created the 
> elevation map is compatible with that running r.los (thinking here of, eg, 
> floating point changes to the data structures).
> 
> >From memory, you are correct that Grass assumes a flat earth and hence is of 
> limited value at the larger scales in which you are interested. Arc doesn't make 
> that assumption. Also, neither system will warn one about doing dubious things 
> like computing a LOS within a lat-long co-ordinate system.
 

Thanks for your comments.   I have found another LOS program that seems to
produce reasonable results, and is geared for vhf/uhf progation by including
a 'k-factor' to flatten the earth by 1.3.  Reads USGS DMA-formatted DEMs,
or it's own format:

	http://www.mindspring.com/~otterson/cs485/


If I can find the time, I'll try a port to use GRASS rasters.
-- 
Tom Poindexter
tpoindex at nyx.net
http://www.nyx.net/~tpoindex/