Chris Hermansen wrote:
...
If I execute:
select geometryType(st_intersection(pblk.geom,pvri.geom))
from pblk,pvri
where pblk.geom && pvri.geom;
I get something quite different than what I expect. I expect to get
polygons, and sometimes multipolygons - which I assume arise when the
intersection process splits up polygons into several constituent parts.
But I also get a bunch of geometrycollections. And these
geometrycollections are apparently empty, for example, the first few
lines of output from the above select:
numgeometries | geometrytype
---------------+--------------------
| POLYGON
| POLYGON
0 | GEOMETRYCOLLECTION
0 | GEOMETRYCOLLECTION
| POLYGON
0 | GEOMETRYCOLLECTION
Are these supposed to be there? What conceivable purpose could they serve?
Hi Chris,
Consider the cases where geometry bounding boxes intersect but the
geometries do not. In these cases, the intersection will be empty. You
probably want to add an additional filter to your query. "WHERE
pblk.geom && pvri.geom AND distance(pblk.geom, pvri.geom) = 0". (You
could alternatively use intersects(geometry, geoemetry), but distance==0
is faster).
Does this help?
-- Kevin
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