[postgis-users] Scale without translate?

[Simon Greener]

Bruce,

> Bruce Rindahl wrote:
>> SELECT translate(
>> scale(
>> translate(the_geom,-x(centroid(the_geom)),-y(centroid(the_geom)))
>> ,myScale)
>> ,x(centroid(the_geom)),y(centroid(the_geom)))
>
> on a side point, is the postgresql optimizer smart enough not to call
> centroid() four times in this case?

You could re-write this as a nested query and compare the performance...

This is a re-write of the select part of your query...

SELECT translate( scale( translate(the_geom,-dx,-dy),
                          myScale),
                   dx,dy)
 FROM (SELECT the_geom as the_geom,
                             x(cent_geom)) as dx,
                            y(cent_geom)) as dy
                 FROM (SELECT the_geom,
                                            centroid(the_geom) as cent_gom
                                 FROM ......you data table...
                     )
      )

regards
S
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