[postgis-users] intersects(), touches(), overlaps() documentation issue

Martin Davis mbdavis at VividSolutions.com
Tue Mar 7 08:56:01 PST 2006

>From your image it looks to me like those lines are not exactly
parallel.  In that case they would only touch, not overlap.

The only way to be 100% certain is if you can post the geometry for the

Touches returns true if the geometries have a point in common, but their
interiors do not intersect.  This is the case if the lines are not quite

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: postgis-users-bounces at postgis.refractions.net 
> [mailto:postgis-users-bounces at postgis.refractions.net] On 
> Behalf Of Amit Kulkarni
> Sent: March 7, 2006 8:38 AM
> To: postgis-users at postgis.refractions.net
> Subject: [postgis-users] intersects(), touches(),overlaps() 
> documentation issue
> All,
> I had a situation where a line overlapped another line for a 
> very small distance near its endpoints. touches() returned 
> true but I was confused why my stored proc was not executing 
> as it should. After some frustrated hours checking inside the 
> loop, I thought to pull up the offending segments in a 
> Desktop GIS and lo! I saw the overlap immediately.
> I was under the impression that touches() returns true and 
> only true if endpoints touched. Is that impression invalid? 
> intersects() returns true but overlap() doesn't return true?
> I am attaching a jpeg. If needed I can attach a .shp
> Thanks for your input
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