[postgis-users] index-based inconsistencies

[Paul Ramsey]

Er, open an issue and attach the relevant supporting files. The
smaller the test table, the better.

P

On Wed, Mar 11, 2009 at 2:04 PM, Paul Ramsey <pramsey at opengeo.org> wrote:
> If you can provide
>
> - a data table dump and
> - a SQL query that returns different results depending on whether
> _ST_Within() or ST_Within() is used
>
> that's enough to debug with. Open an issue in the tracker.
>
> P.
>
> Turn on statement logging in PostgreSQL, then run the Mapserver
> request that causes the
>
> On Wed, Mar 11, 2009 at 1:54 PM, Robert Hollingsworth <reh2 at prodigy.net> wrote:
>> using postgresql 8.3.4
>> using postgis 1.3.3
>> using geos 3.0.0
>> using proj 4.6.1
>>
>> I'm encountering a couple of oddities which I'm pretty sure are related.
>>
>> I have US Census Congressional districts modeled in PostGIS.
>>
>> I've got a simple php program that uses ST_Within( ) to check a lat,lon
>> against the congressional district polygons.  A small number of the
>> districts are causing the query to return zero records incorrectly.
>>
>> I've also got a simple php-mapscript with a LAYER to simply display all of
>> these congressional districts.  When zoomed out around 1:400k and further
>> out, these peculiar districts appear along side their neighbors.  When I
>> zoom in closer, these same districts stop appearing.
>>
>> I'm pretty sure this is a problem with the spatial indexes, which were
>> created by shp2pgsql, because I converted the search program from ST_Within(
>> ) to _ST_Within( ), which is advertised as skipping the indexing.
>> _ST_Within( ) is a bit slower, but finds these districts ok.
>>
>> I've run VACUUM ANALYZE on the table, but this hasn't changed anything.
>>
>> I haven't dug into the mapserver pg driver to see if there is any way for me
>> to manipulate the generated query into skipping indexes.
>>
>> I haven't yet dug into the records further to see if they have pathological
>> bboxes or similar.
>>
>> There are no holes in these polygons.
>>
>> Anyone have any ideas on this?
>>
>> thanks,
>> Robert H.
>>
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>>
>