[postgis-users] Best way to combine a polygon

[Rob Tester]

I have a table with many single ring polygons. Some of the polygons rings in
the table may be contained by other polygons in the same table. What I would
like to do is to assemble all the contained rings into a single polygon. But
it gets a little more convoluted than that. Some of the rings contained by
another poly may contain rings of other poly's too, so:

 

Poly1Ring contains poly2ring, poly3ring and poly4ring

 

Poly2Ring contains poly3ring.

 

What is the best method to combine these polygons to effectively cut holes
where the rings are contained?

 

Thanks,


Rob.

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