[GRASS-user] v.net vector orientation when creating a stream network with gauges

[Moritz Lennert]

On 11/04/16 18:04, Bartolomei.Chris wrote:
> Good morning Markus,
> I'm using GRASS 6.4.4
> I may be stuck using it as the client is running this version instead of GRASS 7 (legacy scripts)
> Do you think running v.net -a would help?

There is no '-a' flag in v.net in GRASS 6.4.4. There is only '-c', but 
that wouldn't make a difference here.

> It may be that there are no nodes at the junction of the little vectors that were added added with the v.net op=connect step (???)

The issue is not the nodes, AFAIK, but the fact that instead of the 
points being snapped to the existing network (as they would be with the 
grass7 '-s' flag), a new connector line between the point and the 
network is created and this connector line perturbs your analysis.

If you are really stuck with grass64 (but please consider Markus' reply 
on that issue), you will have to use a different technique to snap your 
points to the network.

You can use v.distance with upload=to_x,to_y to get the coordinates of 
the closest points on the network and then replace your original point 
locations with those. Cf Micha's mail to you in March [1] which details 
this method.

Moritz


[1] https://lists.osgeo.org/pipermail/grass-user/2016-March/073847.html