On 04/12/2010 23:18, Emma wrote:
Hello,
Thanks for your answer. I think this is exactly what I want
to achieve (sorry I don't have much experience in GRASS).
However I tried:
r.param.scale in=dem out=terrain param=feature s_tol=0.01
and get the error "Lat/Long location is not supported". I
don't really understand why this occurs and what I need to do to
solve the issue. Any idea?
This module runs only in a projected (planar) coordinate system.
This is because in Lat/Lon - with angular coordinates around the
ellipsoid - the concepts of slope and curvature are not really
applicable. So the module can't calculate these basic terrain
parameters.
If you decide that this is the way to go, you'll have to project
your DEM into some other coordinate system, i.e. UTM or whatever is
suitable to your area.
In GRASS, thuis means making a new *projected* LOCATION and a new
MAPSET in that LOCATION. Then start GRASS in that LOCATION and use
r.proj to reproject the DEM from your Lat/Lon LOCATION into the new
LOCATION.
Regards,
Micha
Thanks a lot for your help!
Emma
On 12/04/2010 11:37 AM, Emma wrote:
> Dear all,
>
> Is there a way to calculate from the DEM the total perimeter of all
> lakes (+reservoirs, etc.)? In other words, I need to calculate the
> total length of lake banks and so far could only determine the total
> lakes area, which is of no use in this case.
>
From a DEM directly? No, not that I know. How would you determine what
is a lake, and what is a flat land area? How did you get the area??
Furthermore, sometimes lakes have a slight slope...
Maybe have a look at r.param.scale:
r.param.scale in=dem out=terrain param=feature s_tol=0.01
(or some other very small value)
This creates terrain features: peaks, channels, saddles and flat areas.
The s_tol (slope tolerance) sets how flat an area needs to be before
it's classified as flat.
Once you have devised a method to identify the lakes, then convert those
raster areas to a vector, and the v.to.db module will give you the
perimeter.
It would go something like:
v.db.addcol lakes col="perim double percision"
v.to.db lakes opt=perimeter col=perim units=hectares
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--
Micha Silver
http://www.surfaces.co.il/
Arava Development Co. +972-52-3665918
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