[GRASS-user] Building topologically correct stream network

[stephen sefick]

Markus I believe that would be invaluable.  I will help in anyway that I can.

Stephen Sefick

On Thu, Jul 23, 2009 at 9:25 AM, Markus
Metz<markus.metz.giswork at googlemail.com> wrote:
>
> 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
>>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>>
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-- 
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