[postgis-users] SRID 27492 to SRID 4326

[Nicolas Ribot]

> Hello,
>
> last time i get shapefile witp Porto Portugal streets.
> I convert it to SQL an there was a column with data in SRID 27492.
> I added this data to database, create another column with 4326 SRID and
> transform data from 27492 to 4326 using:
>
> UPDATE axes SET the_geom_wgs = Transform(the_geom,4326);
>
> ok later i expotr file to KML to se it in google earth but the geom is not
> shown in perfect position. It is moved to west south about 80 meters.
>
> I'm sure that data in 27492 is ok. So why after conversion it is not so good
> in google earth? Did I do something wrong? Or forgot about something? Maybe
> there are some additional options to correct it?
>

Hello,
SRID 27492 reads "Datum 73 / Modified Portuguese Grid"
Is it possible that this SRS is based on a grid that is missing in
your PROJ4 installation, and that this grid would give extra precision
when dealing with objects ?

Nicolas