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On 04/12/2010 23:18, Emma wrote:
<blockquote
cite="mid:1FDED903-BD22-4B81-B09A-612944FF8E06@seleeg.org"
type="cite">Hello,
<div><br>
</div>
<div>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: </div>
<div>
<pre><span class="Apple-style-span" style="font-family: Helvetica; white-space: normal;">r.param.scale in=dem out=terrain param=feature s_tol=0.01</span></pre>
</div>
<div>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? </div>
<div><br>
</div>
</blockquote>
<br>
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.<br>
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. <br>
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.<br>
<br>
Regards,<br>
Micha<br>
<blockquote
cite="mid:1FDED903-BD22-4B81-B09A-612944FF8E06@seleeg.org"
type="cite">
<div>Thanks a lot for your help!</div>
<div>Emma </div>
<div><br>
</div>
<div><span class="Apple-style-span" style="font-family: Times;">
<pre>On 12/04/2010 11:37 AM, Emma wrote:
><i> Dear all,
</i>><i>
</i>><i> Is there a way to calculate from the DEM the total perimeter of all
</i>><i> lakes (+reservoirs, etc.)? In other words, I need to calculate the
</i>><i> total length of lake banks and so far could only determine the total
</i>><i> lakes area, which is of no use in this case.
</i>><i>
</i>
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
</pre>
<div><br>
</div>
</span></div>
<div><span class="Apple-style-span" style="font-family: Times;"></span>
<div style="font-family: Times;"><br>
</div>
</div>
<br>
<br>
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</blockquote>
<br>
<br>
<pre class="moz-signature" cols="62">--
Micha Silver
<a class="moz-txt-link-freetext" href="http://www.surfaces.co.il/">http://www.surfaces.co.il/</a>
Arava Development Co. +972-52-3665918
</pre>
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