[GRASS-user] Re: IN: raster-flow-direction OUT:vector-network? (achim)

[achim]

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; I already wrote a script to do it with the
direction raster map, but its slow and it does not allow me to do ii)

ii) I am going to do some statistics on stream lengths /accumulations on
network parts

iii) I need to separate parallel flowing streams from each other which
does not work on my current resolution


I start with pre-produced flow direction, accumulation...

Any workaround idea or scripting tips?

cheers again,
achim


PS: illustration on
http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png

PPS:
> r.mapcalc 'log_accumulation=log(abs(accumulation)+1)'
QUESTION:
why abs? accumulation values should be positive!?

Margherita Di Leo schrieb:
> Hi Achim,
> 
> i usually produce the river network starting from the flow accumulation,
> not from the flow direction. If you have a raster elevation map you can
> get it using r.watershed.
> Then, i make as follows:
> 
> r.mapcalc 'log_accumulation=log(abs(accumulation)+1)'
> 
> r.mapcalc 'inf_river=if(log_accumulation>6)'
> 
> 6 is a treshold value for the log_accumulation, it is a good value for
> me but you maybe can try other values. It produces a binary map.
> 
> Then:
> 
> Raster -> Transform features -> Thin linear features to reduce at 1pixel
> the lines of the binary raster inf_river and create the new file in_river.
> Finally, with r.to.vect you can transform the raster in_river in a
> vector map.
> 
> Hope this helps
> 
> Margherita
> 
>> Message: 8
>> Date: Wed, 20 May 2009 16:45:56 +0200
>> From: achim <ak7 at jupiter.uni-freiburg.de>
>> Subject: [GRASS-user] IN: raster-flow-direction OUT:vector-network?
>> To: grass-user <grass-user at lists.osgeo.org>
>> Message-ID: <4A1417A4.3040701 at jupiter.uni-freiburg.de>
>> Content-Type: text/plain; charset="iso-8859-15"
>>
>> Hello,
>>
>> I am searching for a good idea to convert a raster-flow-direction map
>> into a vector-network map.
>>
>> Probably I will have to write a script. If it is possible at all...
>>
>> In case of writing a script it mean to me: how to produce a line within
>> r.mapcalc?
>>
>> Has anyone a hint?
>>
>> Cheers,
>> achim
>>
>> PS:for illustration I attached a little picture
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