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Martin Davis said at Monday, August 11, 2008 6:07 PM:
> This is a known design flaw in the SimplifyTP algorithm. The problem
is
> that with large tolerance values small holes and shells can wind up on
> the "wrong side" of a containing geometry. It shouldn't be too hard
to
> fix, just by checking whether holes/shells are outside/inside another
> shell, and deleting them if they are.
I had no previous experience with PL/pgSQL, but I put together a
function that seems to work. I'm not at all sure if it is the most
efficient way to do this. In particular, I'm unsure that using
ST_Collect() to append to a geometry collection is efficient as I fear
it might be making a copy of the collection each time. Thoughts anyone?
CREATE FUNCTION ScrubPolygon(input geometry) RETURNS geometry AS $$
declare
outerRing geometry;
innerRing geometry;
innerRingArray geometry[];
count int;
begin
outerRing := ST_ExteriorRing(input);
RAISE NOTICE 'outerRing = %', ST_AsText(outerRing);
count := NumInteriorRings(input);
for i in 1..count
loop
innerRing := InteriorRingN(input,i);
if ST_Contains(ST_MakePolygon(outerRing),
ST_MakePolygon(innerRing)) = 't'
then
innerRingArray :=
array_append(innerRingArray,innerRing);
end if;
end loop;
return MakePolygon(outerRing, innerRingArray);
end;
$$ LANGUAGE plpgsql;
create function ScrubMultiPolygon(input geometry) returns geometry as $$
declare
count int;
geom geometry;
output geometry;
begin
count := ST_NumGeometries(input);
for i in 1..count
loop
geom := ScrubPolygon(ST_GeometryN(input, i));
if output is null
then
output := geom;
else
output := ST_Collect(output, geom);
end if;
end loop;
return output;
end;
$$ LANGUAGE plpgsql;
create function Scrub(input geometry) returns geometry as $$
declare
geom geometry;
output geometry;
begin
if ST_GeometryType(input) = 'ST_MultiPolygon'
then
return ScrubMultiPolygon(input);
elsif ST_GeometryType(input) = 'ST_Polygon'
then
return ScrubPolygon(input);
else
return null;
end if;
end;
$$ LANGUAGE plpgsql;
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