[postgis-users] Indices for ST_distance_sphere

[Stephen Baillie]

G'day Regina,

>It really depends your area of interest, how far out you span out when
>looking for objects and how accurate you want your distance search to be
>what the best solution is.
>
>If your area of interest is small like a state or a UTM zone and even US,
>its best to create a functional index  on ST_Transform(the_geom,
>someplanarsrid) or to just keep your data in that spatial ref and used the
>transformed coordinates for doing distance searches.  If your area is wider
>and your buffer area is also wide, that gets a bit more complicated.
>
>Any rate if you tell us the area you are dealing with - is it all of the
>world, US, Europe etc. and how far you look e.g. do you need to look out 10
>meters from a point, 10 miles or 100 miles or more, then I'm sure we'd be
>more able to give you some direction.
>  
>
My area of interest is Australia (-10 to -50S, 110 to 160E), so I've 
been told that the only spatial ref that it makes sense to use is 
lat/long.  A reasonable ceiling on search ranges is 400km.  Since I'm 
already storing location information in lat/long, I'm not going through 
ST_Transform anyway.

Does that shed more light on my problem?

Thanks,

Steve.

-- 
Stephen Baillie
Developer
Alliance Software

1/234 Whitehorse Road
Nunawading, VIC 3131
Australia

Ph:  03 9877 9921
Fax: 03 9894 2106