#1924: r.watershed - empty stream segment map
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Reporter: jradinger | Owner: grass-dev@…
Type: defect | Status: new
Priority: normal | Milestone:
Component: Raster | Version: svn-trunk
Keywords: | Platform: Linux
Cpu: x86-32 |
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Comment(by mmetz):
Replying to [comment:2 jradinger]:
>
> Two more important things:
> 1) The elevation input map is accutally already a thinned river raster.
The raster
> values represent a pseude elevation which was generated with r.cost
from the source.
> Thus the value (elevation) is increasing upstream. r.watershed is just
used for getting
> the flowdirection and segmenting the river raster. (if needed I can
provide the elevation-rcost
> raster)
r.watershed expects a surface as input. Using a thinned river raster as
input should give weird results: all non-NULL cells face at least one NULL
cell treated as unknown elevation, thus flow direction can not be
unambiguously determined. You can try to place a buffer around the rivers
and fill the buffer with pseudo-elevation values larger than the largest
cost value. For example, create a buffer using 300 meter (3 cells) as
distance, set a pseudo elevation value for the buffer zone, patch the
thinned river raster with the pseudo elevation, run r.watershed with
threshold=3. Works for me.
> And maybe a warning/error message should be printed when threshold = 0,
instead of the (for me confusing error)
Makes sense.
Markus M
--
Ticket URL: <http://trac.osgeo.org/grass/ticket/1924#comment:3>
GRASS GIS <http://grass.osgeo.org>
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