[postgis-users] How to tell if 2 geometries are spatially equal

[Andy Anderson]

Ah. Not a big deal in 2 dimensions, but I have a real problem with  
this in 3D! :-) But I see in OGC 99-049 where they say:

"A Polyhedral Surface is not a MultiPolygon because it violates the  
rule for MultiPolygons that the boundaries of the element Polygons  
intersect only at a finite number of points."

Seems like an unnecessary restriction, but I'm sure they have their  
reasons for excluding this "degenerate" case.

-- Andy

On Jun 3, 2008, at 1:58 PM, Martin Davis wrote:

> Andy Anderson wrote:
>>
>> I'll also note that, to be consistent, this must also mean that  
>> MULTIPOLYGON((0 0, 5 5, 5 0, 0 0), (0 0, 0 5, 5 5, 0 0)) doesn't  
>> have a boundary line at LINESTRING(0 0, 5 5).
> Well, that Multipolygon is actually invalid - since MPs can't have  
> coincident line segments. So the definition *is* consistent!
>>
>> I'm not sure which one that is.
> It's the OGC document 99-049 (the first one you sent)
>
> -- 
> Martin Davis
> Senior Technical Architect
> Refractions Research, Inc.
> (250) 383-3022
>
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