[Qgis-developer] Topology editing in QGis

Martin Dobias wonder.sk at gmail.com
Thu Oct 31 00:28:20 PDT 2013


Hi Denis & Pierre

On Thu, Oct 31, 2013 at 1:45 PM, Denis Rouzaud <denis.rouzaud at gmail.com> wrote:
>
> I put the dev list in copy, since there should be someone arond who's more
> aware on the topic.
> I  saw that Martin Dobias was the committer for the topology editing [0].
> Martin, do you have any suggstion on this?

Let me give some historical context first because I am afraid we are
mixing two different things :-)

For a long time QGIS has some support for "topology editing". But
that's not a proper topology editing as one may think - from
documentation:
"The option  Enable topological editing is for editing and maintaining
common boundaries in polygon mosaics. QGIS ‘detects’ a shared boundary
in a polygon mosaic and you only have to move the vertex once and QGIS
will take care about updating the other boundary."

Originally there were separate map tools for addition, removal and
moving of points which were also doing updates to the shared
boundaries of polygons if the "topological editing" was enabled. The
old commit Denis is referring to was basically meant to add the same
functionality also to the newly created node tool that was meant to
replace the three separate tools.

Now about "real" topology editing of data consisting of nodes and
edges - as discussed already in issue #3483, there are various
topology models (PostGIS topo, GRASS, OpenStreetMap, ...?) that would
need slightly different set of tools and validation methods. I have
not really investigated if it is possible to have a support to cover
all of those models - or even it is worth it. Maybe for a start it
would be enough to pick one and focus just on that (PostGIS topo being
my personal favorite).

In general I would love to see a new "topology" layer type in QGIS
(next to vector and raster) that would bring native topology viewing
and editing capabilities to QGIS. I am not aware of anyone working on
that - if you can spend some time on that matter, I am sure you will
make many people happy :-)

Regards
Martin


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