[geos-devel] predicates on geometry collections supported?

[Chris Hodgson]

What the documentation means to say is that the operation:

Overlaps( geomentryCollection1, geomertryCollection2 )

is not supported. The reason for this is two-fold, as I understand it. 
Firstly, the meaning of the predicates in terms of comparing two 
geometry collections with eachother is not obvious (nor is it defined by 
the "Simple Features" spec), and secondly, I believe there are issues 
with math when you are dealing with collections, that make it impossible 
to robustly and consistently determine the result of the predicates, 
even if the meaning were defined.

However, GEOS _does_ support the operation:

Overlaps( geometry1, geometry2 )

which _is_ defined by the Simple Features spec, and in natural language 
might be described as using a predicate on a collection of geometries 
(namely, the collection containing geometry1 and geometry2). So 
hopefully that answers your question...

Chris

Greg Janée wrote:
> The PostGIS documentation says that predicates such as Overlaps and 
> Contains cannot be used on geometry collections.  But the GEOS homepage 
> says it supports all "Simple Features" functions and operators, and 
> doesn't mention any limitations.  Which is correct?
> 
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