[geos-devel] GEOS & DWithin/Beyond

Martin Davis mbdavis at refractions.net
Tue Jun 12 17:27:14 EDT 2007

I'm not 100% sure of the semantics of DWithin and Beyond, but I assume 
that they test if two geometries are within or further than a given 
distance from each other. 

These seem like complementary functions, so I'm not sure why both are 
provided - but perhaps it's awkward to express negation in Filter?

Anyway, GEOS, like JTS, provides the isWithinDistance method which 
computes this predicate.

As a further note, the reason for having this as a separate predicate 
rather than simply using distance() is that in theory isWithinDistance 
can be optimized more easily and aggresively than distance().

Hope this helps...   Martin

Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022

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