[postgis-devel] Boundary of closed linestrings

[strk]

As it turns out, a closed line has no boundary _by_definition_
according to the OGC Abstract Specification:

 Boolean Closed() -- returns TRUE if this geometry has no boundaries

--strk;


On Thu, Jan 13, 2011 at 02:37:18PM +0100, strk wrote:
> While implementing the topology population functions
> I've stomped of this odd situation:
> 
>  A closed line has no boundary
> 
> Does it seems correct to you ?
> 
> This bug is about one problematic consequence of that:
> http://trac.osgeo.org/postgis/ticket/770
> 
> I'd think a closed line would have a single-point boundary.
> PostGIS thinks ST_StartPoint exists, and ST_EndPoint is the same.
> 
> GEOS returns MULTIPOINT EMPTY for ST_Boundary, and considers
> the endpoint as if they were interior when it comes to DE9-IM
> computation.
> 
> Martin: does JTS agree with GEOS on this ? if so, what's the rationale ?
> 
> --strk; 
> 
>   ()   Free GIS & Flash consultant/developer
>   /\   http://strk.keybit.net/services.html
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  ()   Free GIS & Flash consultant/developer
  /\   http://strk.keybit.net/services.html