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

[Rich Shepard]

On Tue, 10 Apr 2012, Markus Metz wrote:

> Ah ok. In this case it would maybe a good idea if the basins from the
> National Hydrologic Dataset match the basins extracted from the DEM. There
> will most probably not be a 100% match, but it should be a close match.

   I emulated the example at the bottom of the r.stream.extract manual page
step-by-step. This uses the base DEM to identify subbasins. The command line
I used (entered on single line but wrapped in alpine) is:

 	r.watershed -f elev=dem_proj acc=dem.acc drain=dem.drain_dir
basin=dem.basin streams=dem.stream_segs thresh=150000

The threshold established by trial-and-error in comparison with the NHD
subbasins (HUC level 6; black polygons on map1.pdf attached).

   After calculating output raster streams based on unweighted (map2.pdf
attached0 and weighted (map3.pdf attached) accumulation maps, the results
look nothing like the NHD streams (blue lines on map1.pdf attached).

   I have printed the other output maps from r.watershed and r.param.scale.
I've no idea how to interpret them. I would like to post these other maps to
learn how to interpret them and learn why the results of r.stream.extract do
not make sense since they show channels only at the lower elevations or
valleys and not in the mountain range. Is it OK to post these other maps?

Rich
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