[postgis-users] SRID 27492 to SRID 4326

[Fred Lehodey]

Hi Lisek,
http://www.fc.up.pt/pessoas/jagoncal/coordenadas/index.htm

Fred.




On Wed, Nov 19, 2008 at 9:54 AM, Nicolas Ribot <nicky666 at gmail.com> wrote:

> > 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
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