[GRASS-user] Strange behaviour of v.net on GRASS GIS 7

[Markus Metz]

On Thu, Jul 3, 2014 at 1:32 PM, Lluís Vicens <lluis at sigte.udg.es> wrote:
> Hi,
>
> I'm working with GRASS GIS 7.0.0svn (r59969) on Ubuntu 14.04 LTS and I'm
> experiencing a strange behaviour when using v.net. I have set of nodes that
> I want to connect to a collection of streets on a network.
>
> When I execute "v.net streets points=poi out=net op=connect thresh=35" on
> GRASS GIS 6.4.4, the new arc(s)/line(s) that connect the points to the
> network, inherit all the attributes (even the 'cat' value) of the
> pre-existing arcs. But, when I execute the same command on GRASS GIS 7.0.0
> that expected behaviour doesn't take place. The new arc(s)/line(s) generated
> with GRASS 7 doesn't have attributes, a new cat value is generated for each
> new line but they doesn't appear on the attribute table...
>
> I don't know if this is a bug/error, or a different but deliberated
> behaviour.

This new behaviour is by purpose. It does not make sense for a new arc
to inherit the category and attributes of a pre-existing arc. For
example connecting a point to a one-way road could cause the point to
become unreachable because the new arc would also be a one-way road.
If a pre-existing arc is split into two parts, the two new components
should inherit the attributes, but not the categories in order to be
able to assign unique costs to the arcs. See the manual for v.net.path
for an example.

Unless you want to do something particular with these new arcs, it is
usually easier to snap the points to the network instead of creating
new arcs from the points to the network (GRASS 7 only).

Markus M

>
> Thanks in advance.
> Cheers,
> Lluís
>
> --
> Lluís Vicens
>
> SIGTE - Universitat de Girona
> Pl. Ferrater Mora, 1
> 17071   Girona
>
>
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