[GRASS-user] Calculating Length Between Points On Stream Network

[Rich Shepard]

   I have a vector map of a stream network and want to find the distance
between two points on the main stem. I have the geographic coordinates of
each point on the line representing the stream. I tried v.what but I'm not
comfortable that gave me the correct answer.

   The line between the two points is multiple segments where there are
confluences with feeder streams.

   What module, used with the GUI or on the command line, will allow me to
calculate the distance along the stream between two identified points?

Rich