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

[Markus Metz]

On Wed, May 8, 2019 at 2:34 PM Moritz Lennert <mlennert at club.worldonline.be>
wrote:
>
> On 8/05/19 11:44, Martin Landa wrote:
> > Hi,
> >
> > st 8. 5. 2019 v 11:31 odesílatel Moritz Lennert
> > <mlennert at club.worldonline.be> napsal:
> >> 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' ?
> >
> > right, these terms comes from TopoGeo model based described in ISO
13249-3:2006.
> >
> > See eg.
> >
> > http://freegis.fsv.cvut.cz/gwiki/PostGIS_Topology
> >
https://trac.osgeo.org/postgis/attachment/ticket/3046/error_in_getRingedge.png
>
> Right. That does make sens. I didn't think of left and right in that way.
>
> I don't know what use cases are for this feature, compared to the ones I
> listed in my previous mail...

If I understand all this correctly, there is a next_left_edge,
next_right_edge,  previous_left_edge, previous_right_edge. Left would be
equivalent to going CW from the current node, right would be going CCW from
the current node. Next would be the end node, previous would be the start
node.

GRASS example (different from PostGIS terminology): if there are no other
lines connected at the start node of line 1, previous_left_edge =
next_edge_edge = 1, conforming to the GRASS topology model. The
corresponding function to get the next/previous line is
dig_angle_next_line().

Markus M
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