[GRASS-user] selecting upstream river segments

[ivan marchesini]

Dear Grass users,

I have a vector stream network map of a single basin (so only a stream
"tree")...

each stream segment is correctly oriented downstream (the direction of
each vector is from higher to lower elevation..)

I would like to select a random segment of the "tree" and automatically
obtain only the upstream segments.. 
i.e. I would like to obtain a new map containing only the upstream
stream segments of the selected one... (that is the same of removing
those downstream)

obviously I must implement this process into a shell script...

Could you suggest a simple way to solve this little problem? 
Can I use the direction of the vectors to solve this problem?

Many thanks 

Ivan




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Ivan Marchesini
Department of Civil and Environmental Engineering
University of Perugia
Via G. Duranti 93/a 
06125
Perugia (Italy)
Socio fondatore GFOSS "Geospatial Free and Open Source Software" http://www.gfoss.it
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