Yes, Java2D was able to perform a union on the geometries produced by
ST_SimplifyPreserveTopology() and it does the union relatively fast.
The only thing I have found that beats Java2D is ArcGIS. In one test I
did I performed a union of the USGS state boundaries
( Here
are the results:

Oracle 11.1:    25 min
PostGIS 1.3.3:  42 sec
Java2D 1.5:             4 sec
ArcMap 9.2:             1 sec
I just tried this in JTS via JEQL.  Timing for the union was 4 sec.
Any thoughts why PostGIS is about 40x slower than ArcMap at this
As Regina said, the current union operation in PostGIS is quite inefficient. It should speed up a lot once the CascadedUnion algorithm is implemented (which is what the above test in JTS uses)

ArcMap's time is impressive... since they're not open-source it's hard to know what they're doing to get this kind of speed. 8^)

Any thoughts why Oracle takes 25 min? lol

Maybe for a truer metric you should multiply the time by the annual license fee 8^) Of course, this doesn't help Oracle much...

Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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