Yes, that's correct, the geometry relationship predicates are not
available for GeometryCollections. The reason for this is that because
GC's have very loose semantics (e.g. polygons can cross one another
being the main one) it's not possible to robustly & exactly evaluate
some predicates in certain situations.
I guess intersection can always be evaluated correctly, however. With
the new work on prepared geometry, we perhaps could look at widening the
scope a bit. (This might even be supported right now - I can't remember
offhand).
Markus Schneider wrote:
Hello again,
actually I wanted to ask about the "intersects" operator (and not
"intersection") which is used in the given example query.
Markus Schneider wrote:
Hello,
is it correct that geometric operations (especially intersection) are not
available if one of the geometries is a GeometryCollection?
My postgis_full_version() is:
"POSTGIS="1.3.1" GEOS="2.2.3-CAPI-1.1.1" PROJ="Rel. 4.4.9, 29 Oct 2004"
USE_STATS"
When I try to execute the following statement:
SELECT X1.GEOM,X1.NAME,X1.ID FROM MULTITEST X1
WHERE X1.GEOM && SetSRID('BOX3D(174259.098 487844.529, 177282.329
484821.298)'::box3d,28992)
AND intersects (X1.GEOM, SetSRID('BOX3D(174259.098 487844.529, 177282.329
484821.298)'::box3d,28992))
I get the error message:
ERROR: Relate Operation called with a LWGEOMCOLLECTION type. This is
unsupported
SQL Status:XX000
I already digged the source code a bit and found the apparent source of the
message in lwgeom_geos_c.c. It's the check errorIfGeometryCollection(...).
Is there any chance to perform an intersection between a Box and a
GeometryCollection anyway? Or are there plans to implement this?
Thanks in advance,
Best regards,
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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