[GRASS-user] intersection of network-lines and areas

achim ak7 at jupiter.uni-freiburg.de
Mon Mar 2 09:48:51 EST 2009

I have many rivers flow into sinks. For each I'd like to find out, whats
the hole watershed.
Moreover I have some predefined areas (like raster-cells), that must be
devided into their basins (with repect to the boundary cells).

So I have to define the points, where the river-network has its extreme
points/where the points with highest accumulation-values are.

I understand, that I need only one point for r.water.outlet:
-> how do I find out the E and N of the starting-cell? Its a CELL and
there are falling many coordinates within.

-> how do I give r.water.outlet a list of my desired "starting-cells"
(their coordinates)

btw: I tried with those small basins produced by r.watershed to extract
the boundaries crossed by rivers: that didn't work (with what I did). On
the other hand the outled solution would be a bit more precise, if it
would work ;-)


Markus Metz schrieb:
> achim wrote:
>> ...but how can I query my raster-streams in r.water.outlet? I cannot
>> write in all points manually. Do I have to write a script for that?
> You can query the raster streams in the GUI map display, then cut and
> paste the coordinates to r.water.outlet as easting and northing.
> I'm not sure I understood your question correctly, clarification from my
> side: for each river network you need only one point/set of coordinates
> in r.water.outlet, namely the outlet point.
> Regarding your other post, only one cell as output: this would happen if
> the outlet point specified for r.water.outlet is not exactly on the
> stream, but one cell (or more cells) off.
> Going back to the vector approach, maybe v.overlay can help.

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