AW: [postgis-users] Overlaps query

[Robert Coup]

Thorsten Kraus wrote:
>
> Thanks for your answer. I have tried this before.
>
> SELECT COUNT(a.id) FROM tbl1 a, tbl1 b WHERE a.geom && b.geom and a.id 
> <> b.id
>
> But the result differs from my other query. Regarding to the PostGIS 
> doc at http://postgis.refractions.net/docs/ch06.html the && operator 
> does not check the spatial overlap of two geometries, it checks if the 
> bounding boxes of thw geometries overlap. But in my case I need to 
> check if two geometries spatially overlap. Perhaps there is a 
> possibility to make this faster in some way.
>
Try combing the two together - Postgis can use the spatial index to find 
the overlapping bounding boxes, then use the overlaps function to do an 
exact check.

SELECT COUNT(a.id)
FROM tbl1 a, tbl1 b
WHERE a.geom && b.geom
    AND a.id <> b.id
    AND OVERLAPS(a.geom, b.geom)

Rob :)

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