[postgis-users] PostGIS spatial query performance

[Jan Hartmann]

-----Original Message-----
From: postgis-users-admin at postgis.refractions.net
[mailto:postgis-users-admin at postgis.refractions.net]On Behalf Of Dave
Blasby
Sent: Thursday, August 08, 2002 10:50 PM
To: postgis-users at postgis.refractions.net
Dave Blasby wrote:

> select park.* from park,roads
> where
>     expand(box3d(park.the_geom),2) && box3d(roads.the_geom)
>     and distance(park.the_geom, roads.the_geom) <=2;
>
> The base problem is that you are still asking the database to do something
like:

>     For each feature in park
>         see if there are any features in roads that are < 2km away

>  And thats going to take a long time.

Dave, is this really so? It thought it worked as a shortcut operator like &&
in C:

for each feature in park
	see if it overlaps with any feature in roads
		and only if so, compute the distance

As far as I know, lots of optimizing can be done within PostgreSQL by
arranging selects, subselects and explicit joins. This would be especially
important for the Java Topology Suite.

Jan