[GRASS-user] r.stream.extract Syntax Problem

[Margherita Di Leo]

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 <rshepard at appl-ecosys.com>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
>
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-- 
Ing. Margherita Di Leo, Ph.D.
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