[Qgis-developer] Topology editing in QGis

[Radim Blazek]

On Thu, Oct 31, 2013 at 8:39 PM, Sandro Santilli <strk at keybit.net> wrote:
> On Thu, Oct 31, 2013 at 07:30:09PM +0100, Radim Blazek wrote:
>> On Thu, Oct 31, 2013 at 3:28 PM, Sandro Santilli <strk at keybit.net> wrote:
>> > On Thu, Oct 31, 2013 at 09:43:49AM +0100, Radim Blazek wrote:
>> >
>> >> I would prefer something generic from the beginning. We started to
>> >> talk about such common editing interface (PostGIS / GRASS) with strk
>> >> in Zurich. IIRC we were able to find common editing methods. There
>> >> should be some photos of our hand drawn schemas around and strk should
>> >> have a paper with the list of methods. Strk, could you publish a scan
>> >> of it somewhere on Web?
>> >
>> > I'm completely blank about where that piece of paper can be.
>> > Maybe someone took a picture ?
>>
>> This is close to http://linfiniti.com/wp-content/uploads/2011/11/topology.jpg
>> but not the list I mean.
>
> This is another list, which I probably compiled shortly after Zurich,
> but I'm not sure the list on paper was exactly the same (probably not
> as I remember we were fighting about having or not "moveNode" :)
> https://github.com/strk/qgis_pgis_topoedit/wiki/Editing-operations

However editing tools are similar from user point of view, the
implementation of data modification is different because of different
topology models. Non topological editing can be shared by more
providers because elemental editing operations have no consequences.
In topological editing, each simple edit changes also higher level
topology structures and that depends on topology model. It means that
topology editing has to be done mostly in providers.

We want however some common user interface. The question is, if it
makes sense to share more than the same icons? Each topological
provider could have a method returning a list of QAction which would
be inserted to editing toolbox by main application when editing is
started. All editing would be done by provider or better in some
separate class.

In topology editing it is important to visualize topology state of
elements (e.g. free line ends). In GRASS, when editing starts, the
symbology is switched to topology meaning. It would be nice to find a
clean solution how to display both topology state and features
symbolized by attributes. This scheme should also be shared by all
topological providers.

Topology models are usually using multiple geometry types (e.g. nodes,
edges). Multi geometry type layers may also be useful for non
topological layers. How difficult would it be to support multiple
geometry types in a single layer?

Radim