[GRASS-user] distance along flow line to a particular feature

[Godard Vincent]

Hi Grass users,
I am quite new to Grass and I come here to get some hints and guidelines about 
a particular problem I have. 
I work on a watershed (on which I ran r.watershed, to get flow directions, 
accumulation...) and inside this watershed I define a linear feature (raster 
or vector) as the main stream.
I would like to calculate the distance (along the hydrographic network) of 
each pixel of this watershed to the main stream. By distance I mean lenght 
calculated along the flow lines defined by the flow directions. The desired 
final output is a raster containing that distance to the main stream.
Has anybody done such a thing with Grass previously?
Thanks in advance,
Vincent.
-- 
Vincent Godard
 Equipe de géodynamique
 Laboratoire de Géologie
 École Normale Supérieure
 24, Rue Lhomond
 75231 Paris Cedex 05, France
 Tel: +33 1 44 32 22 63  Fax: +33 1 44 32 20 00
 email: godard at geologie.ens.fr