It sounds like you are after computing an overlay of a polygonal dataset.
I might try to first create a set of non-overlapping polygons, then
generate a point for every distinct new polygon and transfer/sum the
attributes from your original polygon table using a point-in-polygon
table join.
Something like this:
http://postgis.refractions.net/support/wiki/index.php?ExamplesOverlayTables
This is not exactly what you want since you are doing a self join with
your polygonal table, but the logic might work for you. Also, there are
probably better ways to produce a set of non-overlapping polygons (like
first setting aside the distinct polygons - "2" in your example below -
to make the query faster).
For example, this query will produce a set of non-overlapping polygons.
SELECT geom AS the_geom
FROM ST_Dump((
SELECT ST_Polygonize(the_geom)
FROM (SELECT ST_Union(ST_Boundary(the_geom)) AS the_geom
FROM my_polygons) AS foo
));
So, yes, it's possible and I'm sure everyone will have a different
approach ... but that's the fun thing with GIS, your options are almost
limitless.
Cheers,
Kevin
Reid Priedhorsky wrote:
Dear all,
I have a set of polygons. Associated with each polygon is a number; call
it score. Each polygon can intersect with zero or more other polygons.
What I would like to compute is a set of non-intersecting polygons with
summed scores -- each of these polygons would be a set of points where
the sum of all the original polygons' scores covered by the result
polygon are equal.
Here's an example in one dimension:
Input:
----3------
----1----
----4----
----2----
Output:
--3--
-4-
-8-
-5-
-4-
----2-----
It is OK if two adjacent result polygons have equal sums.
Can this be done in PostGIS?
Reid
p.s. thanks for the help on my question a few days ago! I felt a tad
foolish after learning it was just a missing isvalid() constraint. I
thought I had one but didn't look carefully enough.
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