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> Union will have the desired effect, but it isn't the most efficient
way
> of dealing with the problem. The most efficient way is to iterate
over
> all the polygons in the MultiPolygon, and drop any which are contained
> in another one in the set.
I'm having a hard time figuring out how to do this, because I cannot
figure out a way to store a set in a local variable. I need to do
something like this:
myset := (select ScrubPolygon(geom)
from (select (ST_Dump(input)).geom) as x);
And then something like this:
output := (select ST_Collect(f1.the_geom) from myset f1, myset f2
where not ST_Within(f1.the_geom, f2.the_geom));
But I cannot figure out how to store the set in a variable. AFAIK, it is
not possible to declare a variable of type "setoff geometry". I also
tried using a temporary table, but there doesn't seem to be a way to
create one in the scope of a function call.
Another approach would be to collect all the polygons into a single
multipolygon and then scrub the nested shells from that, but I have not
found a way to efficiently append a polygon to a multipolygon.
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