Hi Brian,
I have squares. A lot of squares. Thousands of squares. I would
love
to combine them into one or more larger polygons. But, they must
valid
polygons, non-reentrant. For example. if you have a 3x3 grid of
squares,
ABC
RST
XYZ
and I want to combine all but the center, I would need either 2
polygons
(something like ABC and RXYZT), or one polygon with an inner ring.
Assuming there is a table 'squares' containing a geometry type 'the_geom', this
one produces a polygon having an inner ring:
SELECT
ST_Difference(ST_Union(the_geom), (SELECT the_geom FROM squares WHERE id='S'))
FROM squares
Best Regards,
Andreas
Does this return a multipolyon or a single polygon? I didn't state this
originally, but I have disjointed squares. So if you look at a grid:
ABCDEF
OPQRST
UVWXYZ
I might have ABCEFOQUVW
ABC EF
O Q
UVW
So I would want one polygon with ABCQWVU and one with EF
- Brian
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