[GRASS-user] Stream flow direction map

[Nikos Alexandris]

Jarek:
> > > 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

Achim Kisseler:
> > Stream burning: Thats what I thought about.

Nikos: 
> Thanks guys, I'll be testing this quickly (or just pass the information to
> the friend (uses Arc-something-9.3).

Steps tested (more or less successfully):

  # comment: contours were digitised from topomaps with a scale of 1:50000
  # scanned at 300dpi
  # estimated cell size = 4.23 m
  # same scale applies to digitised streams

# set region and rasterise
g.region vect=contours_20m res=4.23m -pa
v.to.rast in=contours_20m out=contours_4.23m

  # comment: this is harder than I thought. Quick checking reveals 
disconnected lines


# set resolution to 1m and (re-)rasterize
g.region res=1 -pa
v.to.rast in=contours_20m out=contours_1m

  # checking... looks ok.
  # I think this particular step is a "crux" for a successful processing
  # any ideas to avoid disconnected lines at a resolution >4.23m?
  # some special downscaling method? Neatest neighbor seems to be a bad choice 
here.


# change resolution as the "1m" will be running for days?
g.region vect=contours_20m res=50m -pa


# contours to elevation
r.surf.contour in=contours_1m out=elevation_50m


# carving...
r.carve rast=elevation_50m vect=streams out=elevation_50m_carved


# extracting streams and direction map (not sure about the threshold)
r.stream.extract elevation=elevation_50m_carved stream_rast=streams_extracted 
direction=stream_directions_extracted threshold=100


# strahler-ordering streams 
r.stream.order stream=streams_extrected dir=stream_directions_extracted 
strahler=strahler

  # resulted streams look a bit squared due to the 50m res I guess. "Strahler" 
looks correct to me (afaict from my studies 6-7 years ago).

Nikos