[GRASS-user] Stream flow direction map

[Nikos Alexandris]

(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