[GRASS-user] Selecting starting points for r.flow

[Ken Mankoff]

Hi Vincent,

Would r.drain work? It allows multiple pairs of initial locations.

I had a similar issue - I wanted to extract a single flowline from a watershed. I think the correct way to do this is r.drain. But I wanted to compare it to results derived from r.watershed, and the flow algorithm from r.watershed and r.drain are different.

My solution was to use r.stream.extract to extract all the streams, and then build a mask, and then run r.drain on the DEM with the mask. This forced r.drain to follow the same flowpaths as those generated from r.watershed.

Perhaps something similar might help,

  -k.

On 2016-12-13 at 17:55, Vincent Godard <godard at cerege.fr> wrote:
> I am using r.flow to generate hillslope flow paths over a high
> resolution DEM. I am actually only interested in a limited number of
> these paths, originating at some selected hilltop points.
>
> r.flow computes flow paths over the whole DEM, and in order to get the
> vectors I am interested in I would need to run the computation over
> the whole region (with skip=1) and select afterward some of these flow
> lines from the output, which is computationally prohibitive on my DEM
> (potentially millions of lines and I am only interested in a few 1000s
> of them).
>
> Is there way to force r.flow to limit the computation to selected flow
> starting points?