[GRASS-user] Hydrological grass question: main channel length for each subbasin

Thomas Adams tea3rd at gmail.com
Sun Feb 16 08:58:33 PST 2014


If you do what you suggest, but first apply a MASK using each subbasin; so,
when you calculate the statistics, they will be for one subbasin at a time;
with a very simple script you could loop through each subbasin.

I hope this helps.


On Sun, Feb 16, 2014 at 11:07 AM, Michel Wortmann
<wortmann at pik-potsdam.de>wrote:

> Hi list,
> I'm looking for a way to calculate the main channel length and width for a
> large number of subbasins within a river basin. I understand that the
> r.stream.* addon / R.basin gives me the main channel length along with a
> tone of other statistics but only for one catchment. Of course, I could
> loop over all my subbasins and calculate the statistics one by one, but I
> fear that will be time consuming and I dont actually need all the other
> analysis.
> I have got an efficient way to calculate the mainstream for each subbasin
> as a vector, but I'm struggling to get from there to the distance of the
> longest segment in each subbasin. Maybe someone has an idea to complete
> this idea of a work flow:
> raster=mainstreams (thinned raster with unique categories for each
> subbasin)
> r.to.vect to vectorise, this unfortunately gives me line segments crossing
> over subbasin boundaries
> somehow make stream segments from each subbasin
> v.to.db to measure the distance of each line segment
> choose the longest distance for each subbasin
> Any suggestions/help would be much appreciated.
> Regards,
> Michel
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