[postgis] Efficiency of a bounding box query vs distance()

[thebanker95065]

Hello all!

I am relatively new to PostGIS, and I haven't found much on this, so 
here goes--

Say I have built the GiST indexes on my table.  I am curious about 
the efficiency of doing a query that checks to see everything inside 
of a predetermined bounding box vs a query that does something 
like 'where distance(the_geom,'POINT(x y)') <25'.  So basically a 
circle radius vs a square box.  I know that there must be more 
calculations going on using the distance function, but I'm curious if 
it is worth it to search with a circular area vs a bounding box.  I 
would think that a circular area is much more cpu intensive, and I 
don't know if GiST indexes will help it.

I hope this makes sense to you all.

Thanks,

Grant


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