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

Michel Wortmann wortmann at pik-potsdam.de
Mon Feb 17 02:16:00 PST 2014

Thanks Tom,
this is what I meant by looping over each subbasin, but that is exactly 
what I would like to avoid as it would take a lot of time for 1000+ 
subbasins and I dont really need all the other analysis.


On 02/16/2014 05:58 PM, Thomas Adams wrote:
> Michel,
> 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.
> Cheers!
> Tom
> On Sun, Feb 16, 2014 at 11:07 AM, Michel Wortmann 
> <wortmann at pik-potsdam.de <mailto: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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