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[udig-devel] Re: Proposals: Topology
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Citing Diatchkov Vitali:
> It is obvious during vector data editing operations it is necessary to
> preserve topological consistence between different vector objects. Feature
> model is not appropriate at all because of there is no topological
> information keeping when each feature is supposed as a standalone feature.
> The case is when two features with polygonal geometries touch each other on
> some common segment of boundary and we change boundary points of one of
> them. Here this operation is hard to trace in respect to the boundary points
> of second feature. I want to move common segment of both features
> simultaneously. When we have simple model of features with geometry without
> topological information it is hard to maintain topological relations.
>
> So the proposal is to build Topology Data Model for such operations from a
> list of simple features with geometry.
Yes, please! I'd like to help with this, if I can.
A good topology API is also on my wish list for three reasons
- topological editing functions as described (no sliver polygons and such)
- I don't like GeoTool's current geometry API, simply because of the fact that
it doesn't use interfaces but uses just plain JTS classes.
- I want 3D geometry and - if possible - 3D topology.
I believe (as does obviously Diatchkov) that it is possible without problems to
also represent non-topological geometries using a topological API. So there
should not be the need for two competeting APIs (topological vs. non-top.)
The third point above (3D geometry) is maybe not your concern, but I'd like to
ensure that any API that is possibly created does at least offer the
possibility to be easly extended to the third dimension. (And I mean real 3D,
not just 2.5D with elevation models.)
Jody wrote:
> Having real topology is better, but hard to do.
Now, I am (as usual) a bit naive, but with my mathematical understanding I don't
see any big problem for creation of such API. (Actually I already tried it ...)
Maybe there are some aspects of it which I don't yet see, which are the "hard"
ones.
One issue that other GeoTools members might have (but not me), is how a possible
Topology API could be related to the GeoAPI geometry interfaces. Are they
topology-aware? Here I need suggestions from the other GeoTools members, how
these concepts could all fit together in GeoTools.
Anyway, I would suggest that you, Diatchkov, attend the IRC session on next
monday (see http://geotools.codehaus.org/Communication), so we can discuss this
topic there.
Matthias Basler
c9bama@xxxxxxxxxxx
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