[postgis] 'real' contains, touches, overlaps etc.

[mbdavis]

You're right, Manuel, conformance to the OGC spec requires relationship
operators that use the DE-9IM model (that is, that understand the difference
between exterior, interior and boundary).    There's also some other subtle
and not-so-subtle issues that need to be addressed in a production-quality
spatial library:

*	Using a finite-precision numerical representation (eg floating point
or integers) can cause a naive implementation to fail badly on certain kinds
of input.  This can be avoided by using robust geometric algorithms.
*	Some kind of spatial indexing or other efficient spatial data
structure need to be implemented if the code is to be usable on inputs with
anything more than a small number of points.
*	The OGC spec has some subtle with how the definition of the spatial
data types interacts with the relationship operators.  A good implementation
should specify how it handles these issues.

JTS is designed to address these issues.  If you're interested in reading
the design specification, which elaborates on these issues and other aspects
of JTS, you can find it at  http://www.vividsolutions.com/jts/jtshome.htm



Martin Davis, Senior Technical Specialist
Vivid Solutions Inc.
Suite #1A-2328 Government Street   Victoria, B.C.   V8T 5G5
Phone: (250) 385 6040    Fax: (250) 385 6046
EMail: mbdavis at vividsolutions.com  Web: www.vividsolutions.com


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