[postgis-devel] GBOXF

[Sandro Santilli]

On Wed, Nov 30, 2011 at 11:47:28AM +0000, Mark Cave-Ayland wrote:
> On 29/11/11 21:51, Sandro Santilli wrote:
> 
> >>Another case to think about would be GROUP BY, which works by
> >>performing an equality comparison between bounding boxes - again,
> >>two very similar yet distinct geometries could be considered equal.
> >
> >This is also true for two very different geometries yet having
> >the same bounding box, so doesn't seem a good example to me.
> >Ie:
> >
> >  LINESTRING(0 0, 10 0, 10 10)
> >  LINESTRING(0 0, 10 10)
> >
> >I guess you were referring once again only to points ?
> 
> No, that would include polygons as well. I'm fairly sure that Paul
> has used the bounding box GROUP BY as part of one of his many
> tutorials.

What I mean is that whenever you use GROUP BY you must know you
are grouping by bounding box equality and for that, it is well
known that two very different geometries can have the very
same bounding box. Seems unrelated to double precision vs. single
precision to me.

--strk; 

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