[GRASS-user] Re: Perimeter of lakes

Hamish hamish_b at yahoo.com
Sun Dec 5 07:02:57 EST 2010

Emma wrote:

Hamish wrote:
> maybe you could calculate the plan-area of the littoral strip
> in a 5m(?) buffer around each one of the lakes and reservoirs?

(set buffer size in proportion to the input data's raster
resolution, although this is still really just an estimation
and not really solving the fractal problem completely)

> Yes, this would be ok too, how can I calculate this? 

If you can find lake edges (or at least lake areas), run
r.buffer or v.buffer on them with the appropriate distance.
r.buffer is more robust, especially in lat/lon, but much more
blocky. As Micha said, picking a local UTM zone to reproject the
lake polygons into can help to reduce a lot of pain, as it's
natural unit is already the meter. In this case I'd avoid
reprojecting the raster data if you can help it.

once the buffers are made, see also r.report and v.to.db modules
for extracting area-in-meters. both work correctly in lat/lon
locations as far as I recall.

> Thanks for your help,Emma 

no worries, good luck



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