[GRASS-user] Building topologically correct stream network

[Markus Metz]

stephen sefick wrote:
> Well, I am not sure what I am going to do.  I would look at the code,
> but I am not adept at C.  Also, I don't know if I understand the
> algorithm, but I think if the topology were complete then it would
> work OK.  I think the 0 orders are unconnected streams- danglers.
>   
Should not happen unless you specified real depressions in r.watershed. 
How did you extract streams?
> This makes sense because they are neither a tributary nor a main stem.
>  The topology is the problem, 
What exactly is wrong with topology? The existence of these dangles?

Markus M
> and I can't figure out how to correct
> this.
> thanks
>
> Stephen Sefick
>
> On Tue, Jul 21, 2009 at 12:34 PM, Markus
> Metz<markus.metz.giswork at googlemail.com> 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
>>>>>
>>>>>           
>>>       
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>>     
>
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