Dear All,
We are trying to generalise our polygon layers which contain sets of polygons
that are perfect partitions of higher level polygons (think of counties in
states which form together a country – a typical case of administrative
hierarchies). The generalisation is only doen for a "view" geometry, we keep on
doing our computations on the original geometries.
The reason is to make a more responsive JS based user interface with OpenLayers
based map interaciton, including brushing etc.
The problem we are facing is that the ST_SimplifyPreserveTopology, while meant
for Polygons, does not assure that the partition is preserved, and we end up
with overlaps between the generalised polygons. What we currently do is:
SELECT DropGeometryColumn('public','mytable','view_geom');
SELECT AddGeometryColumn ('public','mytable','view_geom',4283,'GEOMETRY',2);
UPDATE mytable SET view_geom = ST_SimplifyPreserveTopology(wkb_geometry,0.1);
What is the best way to deal with this? I am sure many of you have faced this
problem. Is there a way to detect the intersections of boudnaries of adjacent
polygons and specify them as strict (immovable) vertices?
My other ideas include:
- Break the polygons into lines, so that the endpoints at intersections are
immutable, and simplify and rebuild the polygons
- maybe try some tricks using the Postgis2.0 planar topology functions
Thanks,
Martin
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