[postgis-users] spatial indices on two geometry or rast columns

[Bryce L Nordgren]

postgis-users-bounces at postgis.refractions.net wrote on 08/11/2011 07:16:22 
PM:

> I?d like to transform these layers to UTM (EPSG 32643). I was 
> thinking of creating a new geometry column for each table and 
> ALTER TABLE wards ADD column geom_utm geometry;
> UPDATE wards SET geom_utm = ST_TRANSFORM(geom,32643);
> 
> Should I, (and can I) create another gist index on the transformed 
geometry?

If you're planning on searching using utm coordinates, I'd make another 
index. If the utm version is just there for reference, I wouldn't bother.

> The same qn applies on a raster table I have called srtm_table ? 
> should I and can I add 
> -          a new ?rast? column called rast_utm with transformed SRID
> in similar fashion above, and then add a gist index on the rast_utm 
column?
> 
> CREATE INDEX ?srtm_table_rast_gist_idx? ON ?public?.?srtm_table? 
> USING GIST (st_convexhull(rast_utm));

This isn't really a different question than the above, since 
st_convexhull(raster) produces a geometry. :) I'd say the same thing: if 
you're going to search using utm coordinates, make a utm index; otherwise, 
no.


Bryce
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