Doing some RTFM I see on the posgis page here:
http://workshops.opengeo.org/postgis-intro/projection.html
"
Note
Be careful of getting too happy with using *ST_Transform* for on-the-fly
conversion. Spatial indexes are built using SRID of the stored
geometries. If comparison are done in a different SRID, spatial indexes
are (often) not used. It is best practice to choose *one SRID* for all
the tables in your database. Only use the transformation function when
you are reading or writing data to external applications.
"
So unless I here otherwise I think above suggests that what I called
option #1 below is the best practice to follow.
On 01/06/2011 06:00 PM, Farrukh Najmi wrote:
Hello,
My application needs to support storing of geometry instances with
different SRID values in the same table and then be able to query it
using spatial operations and a filter geometry which could be in any
SRID.
One possible option (Option #1) is to use ST_TRANSFORM function to
transform all geometry instances on WRITE to the same internal SRID
(say 4326) and transform the filter geometry used by the query to the
same SRID used internally (say 4326) before doing the spatial operation.
The other option (Option #2) is to store all geometry instances with
their original SRID values on WRITE and use ST_TRANSFORM function in
the query to transform all internal geometry instances to match the
same SRID as that of the filter geometry used by the query.
It seems option #1 is less accurately preserving the original data but
is much more efficient on query while option #2 stores original data
without any change but may have serious performance issues due to the
transform on query.
What do people advice based upon their experience with postgis for my
requirement and possible solution.
Thank you for your help.
--
Regards,
Farrukh Najmi
Web: http://www.wellfleetsoftware.com
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