[geos-devel] How robust is GEOS?

[Martin Davis]

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.

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
> > 
> > 	----------------------------------------------------------------
> > 
> > 	 
> > 
> > 	 
> > 
> > 	 
> > 
>