[GRASS-user] Building topologically correct stream network

Margherita Di Leo diregola at gmail.com
Thu Jul 23 09:20:39 EDT 2009

Hi all
Hi Markus,
thanks for your answer. I found that the problem is in the topology of 
the river network. I think that v.strahler produces many '0' because it 
finds many little 'circles' in the stream vector. I tried to produce the 
stream network both with r.watershed -> r.to.vect and with r.strahler.sh 
-> r.to.vect: the results obtained in both ways are very similar. Is 
there a way to eliminate these circles, not by hand ?

Thank you for your time


Markus Metz wrote:
> Margherita Di Leo wrote:
>> I'm sorry but the procedure that I proposed does not produce good 
>> results. In fact the ascii file produced by v.strahler has very 
>> strange orders, and also many 0 (that does not have sense in strahler 
>> order!). I think the problem is generated in finding the outlets 
> Outlet points are where stream is not null and drainage direction is 
> negative, e.g.
> r.mapcalc "outlet_points = if(!isnull(streams) && drainage < 0, 
> streams, null())"
> That would give you outlet points whose cell value is the stream 
> segment number leading to the outlet point.
>> and/or confluences.
> All nodes of the stream vector, excluding outlet points?
> Markus M
>> Waiting for the response of the List (please)..
>> margherita
>> Jarek Jasiewicz wrote:
>>> Hi
>>> maybe this will help:
>>> http://gis.vsb.cz/GIS_Ostrava/GIS_Ova_2009/sbornik/Lists/Papers/060.pdf
>>> it require another gis program but gives great results!
>>> Jarek
>>> Margherita Di Leo pisze:
>>>> Hi Stephen,
>>>> I actually am fighting against almost the same problem, so let's do 
>>>> it together :)
>>>> I found that r.strahler.sh works well to delineate streams and 
>>>> correct topology, (I use a treshold of 1km^2, it works well but 
>>>> don't ask me why :) ), but (in my little experience) does not work 
>>>> to order streams, so I must run v.strahler after r.strahler.sh.
>>>> I know it's a very small hint but hope this helps.
>>>> Best
>>>> margherita
>>>> I have a low relief area in the costal plain of georgia that I am 
>>>> trying to produce a topologically correct stream network. There are 
>>>> many breaks in the flow accumulation grid and I would like to 
>>>> delineate the streams and "correct" the topology after r.thin and 
>>>> r.to.vect have been preformed so that I can then use v.strahler to 
>>>> order the streams. Thanks for any help and I will provide and data 
>>>> that would be helpful. thanks,
>>>> -- Stephen Sefick Let's not spend our time and resources thinking 
>>>> about things that are so little or so large that all they really do 
>>>> for us is puff us up and make us feel like gods. We are mammals, 
>>>> and have not exhausted the annoying little problems of being 
>>>> mammals. -K. Mullis

Eng. Margherita Di Leo
Ph.D. Student 
Methods and Technologies for Environmental Monitoring
Department of Environmental Engineering and Physics (DIFA)

University of Basilicata 
Campus Macchia Romana
85100 - Potenza 

Office: +39-0971205363
Fax: +39-0971205160
E-mail: dileomargherita AT gmail DOT com
Skype: dileomargherita
URL: http://www.difa.unibas.it/A_Manager_PP.do?azione=visualizzaHomePage&id=106

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