[GRASS5] RE: r.los
michael.pelizzari at lmco.com
Tue Oct 17 20:14:20 EDT 2000
Hi, Markus -
r.los seems to work perfectly if the elevation data is UTM. But if the
elevation data is latitude-longitude, like most of my elevation data, the
output map looks like a hollow footprint: mostly "N" for cell values, except
for a few arcs of cells with values like 179 and 180, out where the horizon
might be expected. If indeed these values mark the horizon, why do so few
(if any) cells between these arcs and the observer's cell have non-"N"
I tried a previous Grass version (5.0 beta 6) to see if r.los works with
latitude-longitude-projected elevation data, but the output maps look just
as bad. Sometimes the output map looks like a TV-test-pattern: a really
bizarre pattern of radial lines emanating from the observer towards the
west. Cells in this region have values in the millions or billions (I
forget how many digits). The lines don't converge all the way to the
observer because the radial pattern is cut off along a vertical
(north-south) line. To the east of this vertical line, the cells have
smaller values - typically a few hundred - and form vertical stripes when
when the color map is rescaled to the lower values.
Presumably the TV-test-pattern anomalies plagued only old versions of r.los,
but the hollow footprint anomaly persists in the current version. What am I
doing wrong? Must I convert my elevation data to UTM in order to run r.los?
If so, is there a handy GRASS function to do this?
Thanks in advance,
> -----Original Message-----
> From: Markus Neteler [SMTP:neteler at geog.uni-hannover.de]
> Sent: Tuesday, October 17, 2000 2:00 AM
> To: Pelizzari, Michael
> Subject: Re: r.los
> On Mon, Oct 16, 2000 at 04:39:47PM -0700, Pelizzari, Michael wrote:
> > Greetings, Grasslist -
> > The line of sight calculator r.los does not seem to function as
> > Is "r.los help" incorrect, incomplete, or out of date? I'm using Grass
> > version 5.0 beta 9.
> Hi Mike,
> what's the problem with r.los? It should work...
> Markus Neteler
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