[geos-devel] How robust is GEOS?

[strk at refractions.net]

I've ported the patches to GEOS. Thanks Martin, Kevin.

--strk;

On Fri, May 06, 2005 at 08:03:06PM +0200, strk at refractions.net wrote:
> On Fri, May 06, 2005 at 10:56:33AM -0700, Martin Davis wrote:
> > I would go ahead and implement the patch right now.  It's a very easy
> > patch to apply, and it produces a dramatic improvement in correctness.
> 
> Ok then, can you provide the RobustLineIntersector revision number
> against I should run a diff ? I see only removal of code between
> 1.30 and 1.31 ...
> 
> --strk;
> 
> > 
> > Martin Davis, Senior Technical Architect
> > Vivid Solutions Inc.      www.vividsolutions.com
> > Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
> > Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046
> > 
> > 
> > > -----Original Message-----
> > > From: strk at refractions.net [mailto:strk at refractions.net] 
> > > Sent: May 6, 2005 9:21 AM
> > > To: Martin Davis
> > > Cc: GEOS Development List
> > > Subject: Re: [geos-devel] How robust is GEOS?
> > > 
> > > 
> > > On Fri, May 06, 2005 at 08:43:51AM -0700, Martin Davis wrote:
> > > > Kevin, List, strk:
> > > >  
> > > > I've made an enhancement to JTS (based on a suggestion by 
> > > Kevin) which 
> > > > seems to solve the issue of computed intersection points 
> > > lying outside 
> > > > the intersection of the segment envelopes.  (This is simply one 
> > > > different function in RobustLineIntersector - it's an easy patch, 
> > > > strk).
> > > >  
> > > > This still doesn't produce the ultimate desired result of computing 
> > > > intersections to the full 56 bits of double precision, 
> > > however.  We're 
> > > > working on a solution for that - will post it if and when it's done.
> > > 
> > > Ok. I'll wait for the final version before applying to GEOS. 
> > > Thanks. --strk;
> > > 
> > > >  
> > > > Martin
> > > >  
> > > >  
> > > > Martin Davis, Senior Technical Architect
> > > > Vivid Solutions Inc.      www.vividsolutions.com
> > > > Suite #1A-2328 Government Street Victoria, B.C. V8T 5G5
> > > > Phone: (250) 385 6040 - Local 308 Fax: (250) 385 6046
> > > > 
> > > > 	-----Original Message-----
> > > > 	From: geos-devel-bounces at geos.refractions.net
> > > > [mailto:geos-devel-bounces at geos.refractions.net] On Behalf Of Kevin 
> > > > Wiebe
> > > > 	Sent: May 3, 2005 7:00 AM
> > > > 	To: geos-devel at geos.refractions.net
> > > > 	Subject: [geos-devel] How robust is GEOS?
> > > > 	
> > > > 	
> > > > 
> > > > 	I'm asking for advice here:  What is the most robust 
> > > (numerically 
> > > > stable) way to use GEOS?  What are its limitations?
> > > > 
> > > > 	 
> > > > 
> > > > 	For our purposes we need to use code that is both as fast and 
> > > > accurate as possible.  As you probably know, when using a complex 
> > > > algorithm sometimes even small inaccuracies in geometric 
> > > computations 
> > > > can compound into drastically incorrect results.
> > > > 
> > > > 	 
> > > > 
> > > > 	Here is a concrete example from real customer data:
> > > > 
> > > > 	I have created two simple 2-point LINEs and used the 
> > > GEOS call to get 
> > > > the spot where they intersect:
> > > > 
> > > > 	point = lineA.intersection(lineB);
> > > > 
> > > > 	 
> > > > 
> > > > 	lineA = from (2089426.5233462777,1180182.3877339689) to
> > > > (2085646.6891757075,1195618.7333999649)
> > > > 
> > > > 	lineB = from (1889281.8148903656,1997547.0560044837) to
> > > > (2259977.3672235999,483675.17050843034)
> > > > 
> > > > 	 
> > > > 
> > > > 	the intersection point I get back is this:
> > > > 
> > > > 	point = (2097408.2633752143,1144595.8008114607)
> > > > 
> > > > 	 
> > > > 
> > > > 	This point is a significant distance away from any part 
> > > of lineA.  If 
> > > > one were to place this intersection point between the start and end 
> > > > points of lineA, the resulting line would look ridiculous.
> > > > 
> > > > 	 
> > > > 
> > > > 	JTS returns the same result.
> > > > 
> > > > 	 
> > > > 
> > > > 	Depending on your explanations for this I may have some 
> > > technical 
> > > > advice.
> > > > 
> > > > 	 
> > > > 
> > > > 	Thanks for your comments,
> > > > 
> > > > 	-Kevin-
> > > > 
> > > > 	 
> > > > 
> > > > 	----------------------------------------------------------------
> > > > 
> > > > 	 Kevin Wiebe     Safe Software Inc.              kevin at safe.com
> > > > 
> > > > 	      Senior     Surrey, BC, CANADA       phone: (604) 501-9985
> > > > 
> > > > 	   Developer     http://www.safe.com        fax: (604) 501-9965
> > > > 
> > > > 	----------------------------------------------------------------
> > > > 
> > > > 	 
> > > > 
> > > > 	 
> > > > 
> > > > 	 
> > > > 
> > > 
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