[GRASS-user] Viewsheds

GRASS GRASS user
1

Hi GRASS list,

We are conducting some viewshed analyses at work. We have been using MF
Works for this, but it appears as though it does not account for the
curvature of the Earth. 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.

Thanks in advance.

Paul

2

PA Light wrote:

We are conducting some viewshed analyses at work. We have been using
MF Works for this, but it appears as though it does not account for
the curvature of the Earth. 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.

I am not sure, but I doubt it will; I think you'll have to look through
the source code to get a real answer.

Do check out r.cva, as it's quite a bit better then r.los.
  http://www.ucl.ac.uk/~tcrnmar/

Also consider adding a curvature of the earth adaptation yourself!

Hamish

3

On Tue, 2006-09-26 at 20:39 -0300, PA Light wrote:

Hi GRASS list,

We are conducting some viewshed analyses at work. We have been using MF
Works for this, but it appears as though it does not account for the
curvature of the Earth. 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.

No it does not account for earth curvature. At least I hope not! I use
it for modeling microwave RF propagation and I specifically do not want
earth curvature figured in.

An option to do so, would be nice.

--
Brad Douglas <rez touchofmadness com> KB8UYR
Address: 37.493,-121.924 / WGS84 National Map Corps #TNMC-3785

4

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/&gt; or Benjamin's site <http://www.uni-kiel.de/ufg/ufg_BerDucke.htm&gt;\.

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

5

I would just like to add that the curvature correction feature
has never been tested extensively, so before you want to use
it in a production environment, give it some testing to see
if it gives plausible results (maybe compare with ArcGIS generated
viewsheds)

Benjamin

Mark Lake wrote:

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

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--
Benjamin Ducke, M.A.
Archäoinformatik
(Archaeoinformation Science)
Institut für Ur- und Frühgeschichte
(Inst. of Prehistoric and Historic Archaeology)
Christian-Albrechts-Universität zu Kiel
Johanna-Mestorf-Straße 2-6
D 24098 Kiel
Germany

Tel.: ++49 (0)431 880-3378 / -3379
Fax : ++49 (0)431 880-7300
www.uni-kiel.de/ufg