Hi Rich, AFAIK (but surely Markus Metz will give an insight) r.stream.extract must run with flow accumulation produced by r.watershed. In order to use a weighted flow accumulation, I would produce it using the r.watershed command with the option "flow", instead of mapcalc.
HTH madi On Thu, Apr 5, 2012 at 11:29 PM, Rich Shepard <[email protected]>wrote: > I'm learning to use r.stream.extract by following the detailed example on > the manual page. The last two steps are to extract steam maps using both > weighted and unweighted accumulation maps. The example syntax is: > > # extract streams > r.stream.extract elevation=elevation.10m@**PERMANENT \ > accumulation=elevation.10m.**acc.weighed \ > threshold=1000 \ > stream_rast=elevation.10m.**streams > > And the example syntax to create the weighted flow accumulation map is: > > # weigh accumulation map > r.mapcalc "elevation.10m.acc.weighed = elevation.10m.acc * weight" > > For one of my sub-watersheds I ran the following: > > r.mapcalc "dem10m.acc.weighted = dem10m.acc * weight" > > (all on one line but it may wrap to two lines when you view it). > > I check that this worked properly by displaying demm10m.avg on d.mon x0, > then > displaying dem10m.acc.weighted on the same monitor. The two maps are > congruent. So, > when I run r.stream.extract I get an error that the accumulation map does > not match the elevation map from which r.mapcalc created it: > > r.stream.extract elevation=dem10m.avg accumulation=dem10m.acc.**weighted > threshold=1000 stream_rast=dem10m.streams > > (NOTE: again, all on one line, but may display on two lines.) > > Load input maps and get start points... > ERROR: Accumulation map does not match elevation map! > > There is no error with the unweighted accumulation map (dem10m.acc). > > I'm not seeing why this error is generated, and need to understand why so > I can model a dozen or so small basins. > > TIA, > > Rich > > ______________________________**_________________ > grass-user mailing list > [email protected] > http://lists.osgeo.org/**mailman/listinfo/grass-user<http://lists.osgeo.org/mailman/listinfo/grass-user> > -- Ing. Margherita Di Leo, Ph.D.
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