[GRASS-dev] v.to.db: next/prev line

[Moritz Lennert]

Hi Martin,

Am 8. Mai 2019 08:29:22 MESZ schrieb Martin Landa <landa.martin at gmail.com>:
>Hi,
>
>I wonder whether there is a tool in GRASS which enables writing to
>attribute table information about next/previous lines. Basically info
>about next_right_edge/next_left_edge.
>
>My idea is to extend `v.to.db` option `sides` to work also for lines.
>
>v.to.db mysoils option=roads columns=left,right layer=2
>
>would write into `left` column next_left_edge line category, similarly
>for `right` column.
>
>Does it make sense to you or I am simply overlooking some existing
>tool in GRASS?



I don't think we have a tool for this currently. However, I'm not sure that right and left are relevant terms for this case. Also: what do you do in the case when three lines meet at a node. What would be the 'next_left_edge line' ?

I think this needs a little bit more thinking through...

I think a connectivity matrix between lines could be a possible alternative, as was recently discussed on the lists. Or possibly some form of association table node cats <-> line cats, knowing that will be n-to-n, so maybe best not to be directly integrated into the layers attribute table at least not the nodes' table. From the perspective of lines, one related lower hanging fruit I thought about was to extend v.to.db to include start_cat, stop_cat in addition to the current start/stop which provide the coordinates of nodes. This would then allow to easily identify lines that share common nodes.

Moritz