[postgis-users] ST_Estimated_Extent return incorrect result

[Sufficool, Stanley]

Use insert / update / delete triggers to cache / inflate and deflate the extents of a table in geometry columns?

This comes with a performance price though.

>-----Original Message-----
>From: postgis-users-bounces at postgis.refractions.net
>[mailto:postgis-users-bounces at postgis.refractions.net] On
>Behalf Of Paul Ramsey
>Sent: Friday, August 27, 2010 11:41 AM
>To: PostGIS Users Discussion
>Subject: Re: [postgis-users] ST_Estimated_Extent return
>incorrect result
>
>
>Estimated extent operates by using the ANALYZE statistics,
>which are gathered by sampling. The box returned will always
>be smaller than the actual data extent, because the sample is
>never going to randomly hit all the extrema records.
>
>Rather than using the statistics, which will return an
>underdetermined box, we should probably be top index page,
>which will return an overdetermined box, as that seems to meet
>the use case of the function better.
>
>There's no consistent way to defeat this problem, I usually
>just expand my bounding boxes by 30% and cross my fingers.
>
>P
>
>On Fri, Aug 27, 2010 at 11:27 AM, Denis Rykov <rykovd at gmail.com> wrote:
>> 1. psql -h gis-lab.info -U guest -d osm -c "SELECT
>ST_Extent(the_geom)
>> FROM all_bounds" return correct result:
>>                    st_extent
>> -------------------------------------------------
>>  BOX(-180 35.1298141384262,180 85.4657795616266)
>> (1 row)
>>
>> 2. psql -h gis-lab.info -U guest -d osm -c "SELECT
>> ST_Estimated_Extent('public','all_bounds','the_geom')"
>> return incorrect result:
>>                     st_estimated_extent
>> -------------------------------------------------------------
>>  BOX(-98.0144271850586 35.129810333252,180 85.4657821655273) (1 row)
>>
>> Try to use VACUUM ANALYZE - no results.
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