strk wrote:
On Thu, Jul 01, 2010 at 09:43:33AM -0400, Stephen Woodbridge wrote:
1. working with polygon coverages to maintain boundary coherence during
edits
2. simplify adjacent polygons without leaving gaps between them.
3. editing road networks and maintaining coherence of joined segments
and intersections
While these are more high level application ideas and I guess at the
lowest level you could build a topology that would support any of these,
where did not seem to be support for any higher level functions that
would help support implementing these ideas.
Right, not very management function reach at this time...
For (2) the simplification part it wouldn't be too hard to do.
Currently, if you use ST_Simplify(TopoGeometry) you'd get
an automatic cast from TopoGeometry to Geometry, and _then_
the Geometry would be simplified.
A simple override of that function could instead _first_
simplify components and _finally_ polygonize them togheter
to get you the Geometry. Would that meet your use case 2 ?
For (3) I don't think topology is for you. SQL/MM defined another
model which was "network". Networks have different characteristics
from topology. For example you may have intersections which do
not form nodes (think bridges).
Case (1) is the whole point of keeping the representation of
your data as a topology, but I'm not sure I understand what
you mean by 'during edits'. Postgis topology does have a
validation function you could run after edits, but I guess
your edits would be on the app level. For instance QGIS
itself does use some form of topological representation when
doing edits. Would be interesting to see it cope directly
with topology in the backend.
Well, in general it a good start and I liked what I saw as far as it
went. I think that the biggest problem with it at the moment is
chicken-egg problem of not being mature enough feature wise to be useful
and attract funding to add more to it and not funding or time to move it
in that direction.
If you think about PostGIS and how it has matured over the years and how
much integrating GEOS has done to increase its value as a tool, I think
it is obvious in comparison that we need the topological equivalent of
that effort to build out the topology engine.
The SQL/MM network is another interesting idea I need to look into
because I do a lot with routing.
Thanks,
-Steve
PS. It is great to see you actively involved in with PostGIS and GEOS
again. Thanks for all you past and present efforts.
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