[GRASS-dev] Re: [GRASS GIS] #1577: r.stream.extract/r.stream.order - "calculated" mainchannel vs. "real" mainchannel

[Jarek Jasiewicz]

On 02/15/2012 04:46 PM, Helmut Kudrnovsky wrote:
> what does it means? Any reference? Main channel established in real network
> or algorithms of modeling main channel?
>
> the mentionned "real" mainchannel is the part of real Austrian river network
> (i.e. listed in the annual Austrian hydrographical handbook as the river
> 'Isel')
It is popular argument against algorithmic approach. Usually computer 
algorithms cannot reproduce arbitrary human decisions :-(
>>> an example screenshot of river basin in the eastern part of the alps is
> attached
>
>> where it is?
>
> it's in the ticket, see
> http://trac.osgeo.org/grass/attachment/ticket/1577/mainchannel4.gif
>
> Helmut
Ok, this is not software issue. In attached example calculated main 
channel is evidently longer than real main channel so software cannot 
calculate it different. On my first look there are two possibilities:
- first: main channel is established according to basin area. If so try 
to model stream network using SFD and next Gravelius hierarchy using 
accumulation map as an option. Result should be correct. This is 
impossible using MFD approach
- second: main channel is arbitrary chosen as "central channel". No idea 
how to reproduce it without complex analysis of basin shape and network 
topology.
J.
> -----
> best regards
> Helmut
> --
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