[postgis-users] Spatial query questions

[strk at refractions.net]

On Wed, May 04, 2005 at 09:18:58AM -0400, Bill Binko wrote:
> On Wed, 4 May 2005 strk at refractions.net wrote:
> ...
> > Bounding boxes comparison: true.
> > BBOX are computed for you, either read from cache or computed with full
> > geometry scan. 
> > All geometry types are supported.
> 
> I had a question about this as well: there are methods such as addBBox, 
> hasBBox, etc.  If you run addBBox on a column:
> 
> update tablename set shape_column = addBBox(shape_column);
> 
> Will it help?

You can use summary(shape_column) to see wheter geometries
do or don't have a cache. All but point geometries should
already have one. If this is not your case we can inspect
togheter why (would be a conceptual bug).
addBBOX() on an already bbox-equipped geom would be a no-op.
dropBBOX() would reduce on-disk size, but would slow-down 
sequencial scans and RECHECKS on index scans.
Using addBBOX() on point geometries would be nice to benchmark
(I didn't) as computing the bounding box of a point is probably
*slighty* slower than just using the cached value.

> Bill

--strk;