Thanks for reply, but thats not exactly what I am searching for. I can not to use the accumulation values, because
i) I want to figure out the watersheds on parts of the network (beginning from certain points of the river network to separate some basins on different levels; I already wrote a script to do it with the direction raster map, but its slow and it does not allow me to do ii) ii) I am going to do some statistics on stream lengths /accumulations on network parts iii) I need to separate parallel flowing streams from each other which does not work on my current resolution I start with pre-produced flow direction, accumulation... Any workaround idea or scripting tips? cheers again, achim PS: illustration on http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png PPS: > r.mapcalc 'log_accumulation=log(abs(accumulation)+1)' QUESTION: why abs? accumulation values should be positive!? Margherita Di Leo schrieb: > Hi Achim, > > i usually produce the river network starting from the flow accumulation, > not from the flow direction. If you have a raster elevation map you can > get it using r.watershed. > Then, i make as follows: > > r.mapcalc 'log_accumulation=log(abs(accumulation)+1)' > > r.mapcalc 'inf_river=if(log_accumulation>6)' > > 6 is a treshold value for the log_accumulation, it is a good value for > me but you maybe can try other values. It produces a binary map. > > Then: > > Raster -> Transform features -> Thin linear features to reduce at 1pixel > the lines of the binary raster inf_river and create the new file in_river. > Finally, with r.to.vect you can transform the raster in_river in a > vector map. > > Hope this helps > > Margherita > >> Message: 8 >> Date: Wed, 20 May 2009 16:45:56 +0200 >> From: achim <[email protected]> >> Subject: [GRASS-user] IN: raster-flow-direction OUT:vector-network? >> To: grass-user <[email protected]> >> Message-ID: <[email protected]> >> Content-Type: text/plain; charset="iso-8859-15" >> >> Hello, >> >> I am searching for a good idea to convert a raster-flow-direction map >> into a vector-network map. >> >> Probably I will have to write a script. If it is possible at all... >> >> In case of writing a script it mean to me: how to produce a line within >> r.mapcalc? >> >> Has anyone a hint? >> >> Cheers, >> achim >> >> PS:for illustration I attached a little picture >> -------------- next part -------------- >> A non-text attachment was scrubbed... >> Name: rasterflow-to-network.png >> Type: image/png >> Size: 5162 bytes >> Desc: not available >> Url : >> http://lists.osgeo.org/pipermail/grass-user/attachments/20090520/6198f353/rasterflow-to-network.png >> >> >> ------------------------------ >> >> _______________________________________________ >> grass-user mailing list >> [email protected] >> http://lists.osgeo.org/mailman/listinfo/grass-user >> >> >> End of grass-user Digest, Vol 37, Issue 35 >> ****************************************** >> >> > > _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
