[postgis-users] PostGIS 1.3.3 on Windows XP Unstable

Martin Davis mbdavis at refractions.net
Mon Aug 11 16:07:00 PDT 2008

> well,... hm. Could you put this into trac so we don't lose it? Best
> would be in the GEOS trac, actually (http://trac.osgeo.org/geos) Once
> you get into really large tolerances, preserving topology starts to
> get problematic, for hopefully obvious reasons... I'm not sure how
> robust Martin's routines are supposed to be as tolerance gets really
> big.
> P.

This is a known design flaw in the SimplifyTP algorithm.  The problem is 
that with large tolerance values small holes and shells can wind up on 
the "wrong side" of a containing geometry.   It shouldn't be too hard to 
fix, just by checking whether holes/shells are outside/inside another 
shell, and deleting them if they are.

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

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