[GRASS-user] Re: Perimeter of lakes

Emma emma at seleeg.org
Sat Dec 4 16:18:51 EST 2010


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?

Thanks a lot for your help!

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
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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