[GRASS-user] Building topologically correct stream network

[Jarek Jasiewicz]

Markus Metz pisze:
>
> 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.
Yes, r.to.vect will almost never give correct directional network. It 
require, as Marcus pointed different approach. r.flow ma be a good 
starting point to create new module
Jarek
>
> 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
>>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>>