[GRASS-user] Stream flow direction map

[Jarek Jasiewicz]

Nikos Alexandris pisze:
> (I've switched to KDE (KMail) and still need to get used to sime things - so 
> apologies for not sending this reply to the ml in first place)
>
> Nikos Alexandris:
>   
>>>> While there is a proper (vector) contour map and a very clean stream
>>>> network map (digitised from scratch upon topographic maps of 1:50.000)
>>>> available, the flow direction map is missing.
>>>>
>>>> Is this information easily calculated based on available dem(s), stream
>>>> network(s)? Or should definitely the user add this information while
>>>> digitising the streams?
>>>>
>>>> I have read many past threads wrt "streams, flow, direction,
>>>> accumulation" but could not trace an answer to the above question.
>>>>         
>>> I read again some stuff and I guess that this is a very basic and simple
>>> "hydro-gis" question (for which I do not know the answer):
>>>
>>> is the direction map bound to a specific stream network, i.e. the one
>>> that r.watershed or r.stream.extract produces  or  is it an independent
>>> one, based solely on the input elevation model and its (x-y-z?)
>>> resolution?
>>>
>>> If the latter is true, then it only takes to use either r.watershed or
>>> r.stream.extract to get the direction(s).
>>>
>>> If not, then the question is if the user can supply his own stream map to
>>> r.stream.* modules (specifically to r.stream.extract) in order to get the
>>> desired flow direction map?
>>>       
>
> Jarek Jasiewicz: 
>   
>> Interested question, but I think the easiest answer is carving or stream
>> burining (r.stream.carve). Next reproduce r.watershed or
>> r.stream.extract you shall receive (almost) ideally confidential network
>> with supplied
>>     
>
> Thanks Jarek. This might be (a or the) way to go.
>
> It's not clear to me whether the user can provide his own streams and get the 
> directions let's say from another DEM (with resolution similar to the one of 
> the "source" material from which the streams were produced)? I think that this 
> (should be) is the case.
>
> Ideally, I imagine a module like:
>
>  "v.stream.directions elevation=HighResolutionDEM streams=StreamNetwork 
> output=StreamNetwork_WITH_directions"
>
> Is this rational?
>
> Regards, Nikos
>   
Hmm... not exactly...
How you plan ascribe a scope of different directions to one stream? In 
general stream is not a straight line so in every vertex it can have dir 
pixels directed in any direction. Maybe you need something like 
r.stream.angle? see that module maybe it will help.