[GRASS-user] watershed problem

[ivan marchesini]

Dear users...
I have this kind of problem to solve:

1)I have a point map (pointmap)
 
2)I have a vector river network (rivernetwork) of the main rivers of the
region (each segment has a code)

3) I have a DEM (DEM) of the area

I would like to assign to the pointmap the code of the firs river
segment on which each point of the pointmap hydrologically drain...

I need some suggestions on the process to create.... 
I can create a shell script ... but to do what?? 

I thougth to use r.drain into a shell script but I have two kind of
problems:
a) the elevations of the DEM are integer and r.drain stops when the flow
arrives to the alluvial plain, also after r.fill.dir is executed more
and more time...  
b) how can I find wich is the first segment of the rivernetwork wich is
crossed by the r.drain output???


I hope you can give me some hints!!!!!
thank you very much!!!!!

Ivan




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Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a 
06125
Perugia (Italy)
e-mail: marchesini at unipg.it
        ivan.marchesini at gmail.com
tel: +39(0)755853760
fax (university): +39(0)755853756
fax (home): +39(0)5782830887
jabber: geoivan73 at jabber.org