[postgis-users] distance_spheroid and index files

[RIBOT, Nicolas]

> which gives me all the cities in a 10 km radius around Berlin. 
> Unfortunately, this query takes several minutes as the 
> distance needs to 
> be calculated for every single city, i.e. 60000 times. I read in the 
> PostGIS documentation that this query can be optimised to use the 
> spatial index, but I can't quite figure out how to do it. If somebody 
> could help me out, I'd appreciate that.
> 

I think you should use the "&&" operator to force index usage.

Add a clause to your query to filter out geometries laying inside a 10 km
bounding box.
You are currently computing distance for each geometry even if this geometry
is far away from Berlin.

Try to build a bounding box by expanding the berlin geometry to create a
10km large rectangle.

Hope this helps, and pretty sure someone in the list will be able to show
you how to generate such a BBox for your query.

Nicolas
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