[geos-devel] Is empty LinearRing closed?

[Martin Davis]

But the definition of LinearRing is that the start point equals the end point.   This makes the test unnecessary for a valid LinearRing.  However, maybe it's more general to use the explicit test.

As for an empty LinearRing, well, I don't know of any semantics which covers this.  This might be an angels-on-the-head-of-a-pin kind of thing.  If you don't like the JTS semantics for your particular use-case, you should just implement your own test.

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 
> Mateusz Loskot
> Sent: March 30, 2006 6:25 AM
> To: GEOS Development List
> Subject: [geos-devel] Is empty LinearRing closed?
> 
> 
> Hi,
> 
> As I see, LinearRing is always closed:
> 
> bool LinearRing::isClosed() const {
> 	return true;
> }
> 
> GeometryFactory ::createLinearRing() call creates empty 
> LinerRing. So, should it be considered as closed by default?
> 
> IMO empty LinearRing should not be considered as closed. OGC 
> Simple Feature Spec. says about IsClosed for Curve type (base 
> of LinearRing):
> 
> IsClosed( ):
> (TRUE) if this Curve is closed (StartPoint ( ) = EndPoint ( )).
> 
> 
> So, according to OGC SF Spec. LinearRing::isClosed() should 
> be implemented as follows;
> 
> bool LinearRing::isClosed() const {
> 	return (getStartPoint() == getEndPoint());
> }
> 
> Am I correct?
> 
> Cheers
> -- 
> Mateusz Łoskot
> http://mateusz.loskot.net 
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