[GRASS-user] Building topologically correct stream network

[Markus Metz]

Margherita Di Leo wrote:
> 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 ?
r.strahler.sh tries to if I understand the script right, but there must 
be side effects: what were parallel streams with a ladder may be merged 
into one stream.

Maybe a new module to extract both raster and vector stream networks 
from any flow accumulation map would indeed be useful.

Markus M

>
> 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
>>>>>
>>>>
>>>
>>>
>>
>
>