[geos-devel] GEOS & DWithin/Beyond

[Martin Davis]

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