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 because you can see if the main channel includes the max_ordered stream, and, if not, you can consequently modify the "cost" values assigned.


The syntax:
  v.mainchannel dem=dem xcoor=483456.23 ycoor=234765.33 cost=500,1000,2500,5000,10000 input=input_map output=output_map 




Ivan Marchesini and Annalisa Minelli, Univ. Perugia.

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