[postgis-users] Intersection problems with complex polygons

[Andreas Neumann]

Hi,

I regularly run into intersection problems when using intersection 
between a rectangle (defined as a POLYGON) and a very complex polygon 
(MULTIPOLYGON).

After intersection I expect to get back a MULTIPOLYGON, however, it 
results in a GEOMETRYCOLLECTION not only containing POLYGON or 
MULTIPOLYGON elements, but also LINESTRINGs.

I can't understand why? is there a limit in complexity or a bug in the 
GEOS library?

To reproduce my problem I have a SQL query online, containing the two 
geometries: http://www.carto.net/neumann/temp/intersection_test.sql.gz - 
the first geometry is fairly complex, but a realworld example from the 
Yosemite National Park.

I am using the latest GEOS library (2.1.1) and the latest postgis 
version (0.9.1).

Any hints would be welcome.

Thanks,
Andreas