[postgis-users] Indices for ST_distance_sphere

[Stephen Baillie]

>What about 3112 (# GDA94 / Geoscience Australia Lambert) or 3577
>(Australian Albers), those should cover things fine, no?
>  
>
Possibly, although I'm finding it hard to find hard data on what those 
actually mean (let alone what other alternatives are supported by 
PostGIS).  It looks like they still produce range distortion, which 
answers to my previous question on this list gave me to believe would be 
a problem for anything except true spherical distances.

Closer to the point, though, the choice of projection is of lesser 
importance to my question than that of indexing.  PostgreSQL tells me 
that the spherical distance calculations increase full table scan time 
by about two-thirds when I use those as the where clause of my search 
instead of using a lat/long bounding box, but my question is actually 
about indexing before doing such distance calculations:

Is it possible to create an index that can be used to speed searches 
based on distance from an arbitrary point, or should I just use a 
lat/long bounding box?

Thanks,

Steve.

-- 
Stephen Baillie
Developer
Alliance Software

1/234 Whitehorse Road
Nunawading, VIC 3131
Australia

Ph:  03 9877 9921
Fax: 03 9894 2106