[GRASS-user] Building topologically correct stream network

Markus Metz markus.metz.giswork at googlemail.com
Tue Jul 21 13:34:57 EDT 2009

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, 

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

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