[postgis-users] database transformation

[Paolo Rizzi]

If your data is already correct, you should _not_ use transform().
You should simply force the new SRID, using something like:
	UPDATE  table_name SET geom=ST_SetSRID(geom,3763)

So if you have a coordinate like 1234567.890123, that is correct
for Portugal in the old 27492 SRID and also in the new 3763,
you must not transform it, but simply tell PostGIS that now
the SRID is 3763.
If you use transform, you may end up with a changed coordinate,
that is no longer valid.
If, instead, the coordinate 1234567.890123 is _not_ valid
in the new SRID 3763, you have to transform it, but beware that
the trasformation may not go well.
If the old SRID was deprecated, there may be errors in its definition,
so the transform may give you odd results...

Bye
Paolo


> Hello everyone,
> 
> I have a database created with the program pgadmin3. The geo-referencing 
> system is the Datum 73 / Modified Portuguese
> 
> Grid (deprecated) "EPSG: 27492" and wanted to change the whole database 
> to the coordinate system ETRS89 / Portugal TM06 (EPSG: 3763).
> 
> How can I make this transformation?
> 
> Thank you for your help
> 
> -- bernardo --
> 
> 
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