[GRASS-user] flow accumulation values

Markus Metz markus.metz.giswork at gmail.com
Wed Aug 31 13:42:44 PDT 2016

On Fri, Aug 26, 2016 at 9:56 AM, Micha Silver <micha at arava.co.il> wrote:
> I also noticed that r.stream.extract finds different flow-paths than
> r.watershed, which complicates comparisons between the two. The work-around
> for this is to use a mask to force r.stream.extract to find the flow-path
> you want.
> r.stream.extract is the preferred stream extraction tool.
> OK, but a flow accum raster is required for running r.stream.order (which
> outputs flow_accum) and AFAIK, the only way to get a flow_accum raster is
> with r.watershed.
> ??
> BTW, I'm not the only one who has encountered this:
> http://gis.stackexchange.com/questions/201118/how-to-obtain-accumulation-map-from-r-stream-extract

The main purpose of r.stream.extract is to extract a stream network
from any flow accumulation map and elevation map. The flow
accumulation map can be produced with any other tool that is able to
accumulate flow, and that tool does not need to be a GRASS module,
e.g. TAUDEM output is also fine. Further on, any flow accumulation can
be further processed before being used as input for r.stream.extract.
For example, valleys identified by some curvature analysis could be

r.stream.extract can also work with only elevation as input. In this
case flow accumulation is done internally similar to r.watershed. If
you need flow accumulation, it must be calculated first and then used
as input for r.stream.extract.

Markus M

> Thanks,
> Best,
> Micha

More information about the grass-user mailing list