[postgis-devel] automatic BVOL on spatial columns

[strk at refractions.net]

On Thu, Dec 30, 2004 at 10:00:21AM -0800, Paul Ramsey wrote:
> Sounds good and simple to me, good stuff!
> 
> P

Good. I'll take that path then.
Note that it won't be a quick operation (see report on the
various functions and their bbox cache behaviour.

--strk;

> 
> strk at refractions.net wrote:
> 
> >I've made canonical, (E)WKT and (E)WKB and GEOS input methods
> >call a function returning wheter it's worth to cache bbox, and
> >add it accordingly. None of this methods will face the problem
> >of wheter to drop an existing cache, as transport formats do
> >not contain that information. GEOS Geometry could potentially
> >store an Envelope, but that's not automatically converted by
> >the existing converters.
> >
> >Note that many geometry editors decide wheter or not to
> >add a bbox cache to their return based on other heuristics.
> >Some of them add a bbox if its input geom does have a cache
> >already ( transform, translate, reverse, simplify, segmentize ),
> >some always avoid a bbox computation ( collect, addpoint ).
> >
> >To make this behaviour consistent every function returning
> >a geometry should call the heuristic functions and explicitly
> >cache a bbox when the conditions match. 
> >
> >Still I'm convinced that the user should have more control
> >over this aspect, more specifically she should decide when
> >exactly to compute it in a chain of calls, to improve performace.
> >Users willing to have this finer control can set AUTOCACHE_BBOX
> >to 0 in Makefile.config. In this case internal functions should
> >compute a bbox only if that is a simple operation (ie: does not
> >require a scan of the geometry points). The implemented trigger
> >would be then useful to ensure that tables used for frequent
> >selects always have a bbox cached.
> >
> 
> 
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