[postgis-users] point_ops with GiST PostGIS Spatial Index

[Paul Ramsey]

point_ops has nothing at all to do with PostGIS, it's an opclass for
the internal 'point' type of PostgreSQL (let confusion reign).

You may find that you get better PostGIS plans with 2.1 when it comes
out, as the selectivity calculation logic has been refined a bit
further. I strongly doubt you'll get any good love at all from the
PostgreSQL point type and point_ops, as no real work on selectivity
for the vector types has been implemented in core PostgreSQL.

P.

On Wed, Jun 5, 2013 at 5:05 PM, BladeOfLight16 <bladeoflight16 at gmail.com> wrote:
> Pardon my lack of specificity. I'm familiar with spatial indexes and at
> least somewhat familiar with ST_Contains and its internal bounding box
> check. Maybe it would help to clarify why I found this point_ops operator
> class so interesting. Currently, my queries are often getting bad estimates
> for the number of rows the spatial index will return. On a sample set of
> data (roughly 500K rows), EXPLAIN ANALYZE will show that the estimator
> thinks it will return 1 row when it actually returns over 10,000. I've been
> meaning to come up with a SSCCE to report as an issue but haven't had time.
> (I still intend to, when I can.) So when I saw this, I thought maybe it's
> something I can implement quickly to try out and see if it changes anything.
> So I'm trying to figure out what I need to do to try it out (if it's even
> possible).
>
> So when that index is created, is PostgreSQL/PostGIS somehow figuring out
> that my geometry consists of points only and using the point_ops operator
> class, or is it just using the operator class that goes with && (bounding
> box overlap operator), or are those operators in the same class? I'm pretty
> much lost on which operators and indexes go with what classes. (point_ops is
> the only operator class I've even heard of.)
>
> Thanks again.
>
> On Wed, Jun 5, 2013 at 2:50 PM, Tambade, Kedar <ktambade at cghtech.com> wrote:
>>
>> Create the gist index on table containing points using the following
>> syntax:
>>
>>
>>
>> CREATE INDEX <index name> ON <table name> USING GIST (<geometry column
>> name>);
>>
>>
>>
>> After the index is created use the criteria st_contains(polygon,point)  in
>> the where clause of select statement:
>>
>>
>>
>> Select * from <tablename> where st_contains(polygon, point) ;
>>
>>
>>
>> Regards,
>>
>>
>>
>> Kedar Tambade
>>
>>
>>
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>>
>> From: postgis-users-bounces at lists.osgeo.org
>> [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of BladeOfLight16
>> Sent: Wednesday, June 05, 2013 2:29 PM
>> To: PostGIS Users Discussion; pgsql-general at postgresql.org
>> Subject: [postgis-users] point_ops with GiST PostGIS Spatial Index
>>
>>
>>
>> I posted this question on StackOverflow, and the only person to answer
>> recommended I ask these lists for more details and link to the question:
>>
>> http://stackoverflow.com/questions/16927331/postgresql-point-ops-with-gist-postgis-spatial-index
>>
>> My question is:
>>
>> The 9.0 release notes for PostgreSQL states the following change:
>>
>> Add point_ops operator class for GiST (Teodor Sigaev)
>>
>> This feature permits GiST indexing of point columns. The index can be used
>> for several types of queries such as point <@ polygon (point is in polygon).
>> This should make many PostGIS queries faster.
>>
>> I have a very large table (millions of rows) with a GEOMETRY(POINT,[SRID])
>> column that I sometimes compare to polygons. Do I need to do anything to
>> enable this when creating the index? Do I have to use the operator
>> indicated, or would this work with ST_Contains which uses && internally?
>>
>> Thanks for any help.
>>
>>
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