[GRASS-user] Snapping river segments

[Maciej Sieczka]

Colin Nielsen wrote:
> I'm trying to extract only the largest rivers from a very detailed
> hydrology map (mostly for display purposes). Right now the map just
> looks black with lines. I've managed to use v.extract for areas but
> since the rivers are in segments i can't use v.extract for lengths.
> I've tried v.clean snap but it doesn't seem to be doing what I want it
> to. Any advice?

v.build.polylines

There are bugs in 6.2 in this module (easy to workaround, and fixed for
good in 6.3 by Martin Landa):

https://intevation.de/rt/webrt?serial_num=4249
Workaround: run 'v.clean tool=prune thresh=0' on the v.bulid polylines
output. It will remove the bogus doubled vertices.

https://intevation.de/rt/webrt?serial_num=4247
Applies only to boundaries anyway.

After you transform segmented lines into polylines you should be able
to use v.extract by length.

Maciek