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<div>Great, </div>
<div>just wanted to calibrate the thinking :-)</div>
<p align="left">/Nicklas<br />
<br />
2010-08-17 Olivier Courtin wrote:<br />
<br />
<br />
>On Aug 17, 2010, at 1:35 PM, Nicklas Avén wrote:<br />
><br />
>Nicklas,<br />
><br />
>> in #568 you write:<br />
>> "As a consequence closed surface (so volume) have a 0 perimeter <br />
>> value return"<br />
>><br />
>> Is it so. Isn't it nessecary to be able to describe a closed survace <br />
>> without handling it as a volum or polyhedron?<br />
>> I mean like a closed linestring. Sometimes you just want a closed <br />
>> linestring not a polygon.<br />
>><br />
>> I thought this was to opff topic in #568 so I put it in a separate <br />
>> post.<br />
>><br />
>> Does the spec say anything about this?<br />
><br />
>Well in fact in ISO 19107 we have all the kind of geometries we could<br />
>dream in GIS field fully describded.<br />
>And so we've got points, curves, surfaces, solids, conic and so on...<br />
><br />
>Right now this full model is really ambitous.<br />
>(This model is also used in GML 3, and so in CityGML)<br />
><br />
>Current spatial databases standard only take a part of it.<br />
>(Even if we have strong clues that the next one will take in count<br />
>the full ISO 19107 model.)<br />
><br />
>And in fact PolyhedralSurface or TIN are initialy surfaces.<br />
>So by analogy they behave more like your linestring (who could be <br />
>closed).<br />
><br />
>And still by analogy your polygon equivalent in 3D is a solid<br />
>in ISO 19107, but there's still no database standard to describe it.<br />
><br />
>So the best we have right now (in spatial database standards) is 3D <br />
>closed surface...<br />
><br />
><br />
>> The difference shows for example when we measure distance from a <br />
>> closed survace/volum<br />
>> to a point inside it. If it is a volum the distance is 0 if it is <br />
>> just a closed surface there is a distance<br />
>> to calculate to the closest facet.<br />
><br />
>I'm agree with you that's a really good idea to have<br />
>a flag to indicate on the geometry if it's closed or not (volume or <br />
>surface)<br />
><br />
>I've just began to think on a topology serialization,<br />
>need to work on it far more...<br />
><br />
><br />
>--<br />
>Olivier<br />
><br />
><br />
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><br />
> </p>
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