[GRASS-user] Extract subnet from grass vector network based on selected nodes

[Moritz Lennert]

On 28/09/17 08:51, Markus Metz wrote:
> 
> 
> On Wed, Sep 27, 2017 at 11:55 PM, Moritz Lennert 
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be>> wrote:
>  >
>  > On 27/09/17 21:03, Markus Metz wrote:
>  >>
>  >>
>  >>
>  >> On Wed, Sep 27, 2017 at 4:07 PM, Moritz Lennert 
> <mlennert at club.worldonline.be <mailto:mlennert at club.worldonline.be> 
> <mailto:mlennert at club.worldonline.be 
> <mailto:mlennert at club.worldonline.be>>> wrote:
>  >>  >
>  >>  >
>  >>  >
>  >>  > Le 27 septembre 2017 13:11:54 GMT+02:00, Johannes Radinger 
> <johannesradinger at gmail.com <mailto:johannesradinger at gmail.com> 
> <mailto:johannesradinger at gmail.com <mailto:johannesradinger at gmail.com>>> 
> a écrit :
>  >>  > >Hi,
>  >>  > >
>  >>  > >I have a GRASS vector network that represents a river network (with
>  >>  > >many
>  >>  > >first order tributaries) and that has additional connected nodes 
> that
>  >>  > >represent sampling sites.
>  >>  > >
>  >>  > >I'd like to extract a minimum subnetwork of the full network 
> that still
>  >>  > >connects a set of selected nodes (e.g. identified by their cat).
>  >>  > >However,
>  >>  > >network edges (i.e. river segments) that are not necessary to 
> connect
>  >>  > >the
>  >>  > >sampling points should be excluded in the new subnetwork. Is there a
>  >>  > >function or process in GRASS GIS to extract such a subnetwork that
>  >>  > >fully
>  >>  > >connects a set of selected nodes?
>  >>  >
>  >>  > not sure but maybe v.net.spanningtree ?
>  >>
>  >> v.net.spanningtree calculates a tree covering all nodes in the 
> network, not only selected nodes, therefore v.net.spanningtree does not 
> apply here.
>  >
>  >
>  > If you connect only the selected nodes to the network, wouldn't that 
> work ? Or does v.net.spanningtree consider all connections between lines 
> as nodes ?
> 
> v.net.spanningtree considers all internal nodes of the network. See also
> https://en.wikipedia.org/wiki/Spanning_tree

Ok, thanks. So, one would need to "disconnect" lines at non-selected 
nodes for this to work.

And maybe some clarification on what is meant by "nodes" in the sentence 
"A spanning tree is a minimum cost subnetwork connecting all nodes in an 
undirected network" in the man page might help future users.

Moritz