[postgis-users] The operator && is not overlapsoperator basedonthe OGC SF SQL

[Darko Androsevic]

Hi Paul,

Thanks for the clarification and I think that I got the definition from your
answer.

"&&" follows the OGC's intersect operator semantics on geometries' *bounding
boxes*.


This means that if one has only bounding boxes geometries then this is valid
"geom && candidate" <=> "geom && candidate AND intersects(geom,candidate)"


Cheers,
Darko



-----Original Message-----
From: postgis-users-bounces at postgis.refractions.net
[mailto:postgis-users-bounces at postgis.refractions.net]On Behalf Of Paul
Ramsey
Sent: Wednesday, August 18, 2004 9:49 AM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] The operator && is not overlapsoperator
basedonthe OGC SF SQL


Just to clarify Darko: you are aware that the && test applies *only* to
the geometries *bounding boxes* not to the geometries themselves, right?
We use the && operator only for a "first pass" thinning of candidate
geometries, which are then passed to the more intensive GEOS testing.
("geom && candidate AND intersects(geom,candidate)")

Is the exact semantic of the bounding box test still important to you?

Darko Androsevic wrote:

> Hello Nicolas,
>
> Thanks for the quick answer. However, I have to ask you for one additional
> thing.
>
> Nicolas wrote:
> "&&" tells if 2 geometries' extents overlap or not."
> Since we agree that it IS NOT the OGC overlap, I would appreciate if you
> could you please define the bounding boxes "overlap" in the postGIS
context
> or point me where it might be precisely defined?
>
>
> BTW, I still think, based on my small set of simple test queries, that it
> actually follows the OGC's "intersects" = "not disjoint" operators
sematics.
> Why is this important to me?
> I would like to use it in combination with GEOS extensions to get the OGC
> operator semantics.
> For example, if it is defined as the OGC intersect then one does not have
to
> use the additional GEOS intersect extension in case of the OGC's intersect
> query and improve performance.

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