[geos-devel] How robust is GEOS?

[strk at refractions.net]

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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>