On Thu, Sep 28, 2017 at 9:43 AM, Moritz Lennert < [email protected]> wrote: > > On 28/09/17 08:51, Markus Metz wrote: >> >> >> >> On Wed, Sep 27, 2017 at 11:55 PM, Moritz Lennert < [email protected] <mailto:[email protected]>> wrote: >> > >> > On 27/09/17 21:03, Markus Metz wrote: >> >> >> >> >> >> >> >> On Wed, Sep 27, 2017 at 4:07 PM, Moritz Lennert < [email protected] <mailto:[email protected]> <mailto: [email protected] <mailto:[email protected]>>> wrote: >> >> > >> >> > >> >> > >> >> > Le 27 septembre 2017 13:11:54 GMT+02:00, Johannes Radinger < [email protected] <mailto:[email protected]> <mailto: [email protected] <mailto:[email protected]>>> 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.
or use v.net.steiner (see my previous reply) > > 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. Yes, that would help. I needed to look at the library fn NetA_spanning_tree() to be sure. Markus M > > Moritz
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