[postgis-users] Filter 3D points with postgis, st_disjoint st_intersects

[Paul Ramsey]

No, ST_Intersects is just a 2D only operation. Extra dimensions are
not accounted for.

Once you get into operations on polygons, it becomes impossible to do
3D ops, since the 3D volumetric shape of a polygon-with-zs is
ambiguous for most cases.

P.

On Tue, Oct 13, 2009 at 11:33 PM, Brian Modra <brian at zwartberg.com> wrote:
> 2009/10/14 Bruno Friedmann <bruno at ioda-net.ch>:
>> Hi all, I've just discover that I've a trouble (another) with 3D.
>>
>> I've 2 set of records, one is full, the other have some hole inside.
>> I'm looking a way to extract ( building some 3d polygons or 3d lines ) point that are in the first full set, not present in the
>> second. ( Find the hole )
>>
>> I was thinking about using st_intersects &| st_disjoint but I realize that
>>
>> select st_disjoint(
>> st_setsrid(st_makepoint(585000, 226500, 0),21781),
>> st_setsrid(st_makepoint(585000, 226500, 100),21781)
>> )
>> ,
>> st_intersects(
>> st_setsrid(st_makepoint(585000, 226500, 0),21781),
>> st_setsrid(st_makepoint(585000, 226500, 100),21781)
>> )
>>
>> return false,true ... which should return true,false.
>
> I think whats happening is that although the coords are stored
> x,y,z... the calculations project them first.
> So its not a 3D comparison.
>
>>
>> Did I need to invent my st_intersects3D function which would you st_intersects with X,Y and an another check on Z equality ?
>>
>> Did you think it's a good idea.
>>
>> PS : I'm using postgis 1.3.5 now, did the 1.4.0 release could help me in this case ?
>>
>> Many thanks in advance for your precious advise
>>
>>
>> --
>>
>>     Bruno Friedmann
>>
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>>
>
>
>
> --
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