v.mainchannel Finds the main channel of a basin starting from the
vector file of the stream network. As first you have to visualize on the
GRASS monitor the vector map which you want to calculate the main channel
for; with a scale (so you can realize the distances between the closing
section and the sources) you can choose some values for the cost isolines
(from the outlet); then you can individuate (by interrogating a DEM
underlying the vector map) the outlet cross section coordinates. These
coordinates, the selected cost values and the input/output map names have
to be given in input to the program.
The program returns the main channel considering two factors:
distance: often the main channel is the longest track in the network
height: the source of the main channel is conventionally taken as
the highest
This module can be used for any ordinary vector stream network, but the
analysis becomes particularly interesting if you have a vector stream
network ordered by Horton-Strahler (e.g. derived from
v.strahler or
r.strahler.sh) because you can see if
the main channel includes the max_ordered stream, and, if not, you can
consequently modify the "cost" values assigned.
