[GRASS-user] Re: IN: raster-flow-direction OUT:vector-network?
ak7 at jupiter.uni-freiburg.de
Wed Jun 10 09:27:07 EDT 2009
by the way, I solved my problem and want you to participate. If you are
interested in the script, just write back.
To get a network from a direction file I
- first made a raster file with a resolution tree times higher
- then I made eight raster files from this, one for each direction
- I added connecting, desired raster cells
- them r.to.vect
- and then I patched
(see attached picture)
Advantage in contrast to r.thin: even directly neighboring cells can be
considered. No little areas appearing and no shortcuts are made.
Hopefully helpfully for anyone,
PS: my directions
# 3 2 1
# 4 X 8
# 5 6 7
Markus GRASS schrieb:
> achim wrote:
>> Thanks for reply,
>> but thats not exactly what I am searching for. I can not to use the
>> accumulation values, because
>> i) I want to figure out the watersheds on parts of the network
>> (beginning from certain points of the river network to separate some
>> basins on different levels;
> r.water.outlet would do that, granted that flow direction has the same
> format like r.watershed's flow direction
>> ii) I am going to do some statistics on stream lengths /accumulations on
>> network parts
> Is the suggestion by Margherita Di Leo to get streams not working?
>> iii) I need to separate parallel flowing streams from each other which
>> does not work on my current resolution
> I think v.generalize can separate parallel lines with method=displacement.
>>> r.mapcalc 'log_accumulation=log(abs(accumulation)+1)'
>> why abs? accumulation values should be positive!?
> Depends on the module used to create flow accumulation. r.watershed
> produces negative flow accumulation values for areas where flow
> accumulation is a likely underestimate (basin extending beyond region
> extends or parts of the basin are masked out). Also see r.watershed manual.
> The mapcalc approach may not work well on MFD accumulation maps; there
> the stream output of r.watershed would help.
> Markus M
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