[Gvsig_english] project between datums

[Diego Guerrero Sevilla]

Hi, Julien.

The manual transformation should work if you know the correct parameters. Any 
transformation (EPSG, manual, nadgrid) is useful only if the implied CRSs 
have diferent datum. When the datum is the same you don't need a 
transformation, you only need a conversion operation between two projection 
systems (Automatly performed by gvSIG when you select diferent CRSs for the 
view and a layer).

EPSG data base don't have a transformation between NTF(paris) and WSG84 
(http://www.epsg.org --> Geodetic dataset) so in gvSIG the transformation box 
is empty for CRSs whit these datums.

Best regards,

	Diego.

On Wednesday 09 January 2008 18:45:55 ju wrote:
> thanks sergio but i already try !
> in arcgis, there is a transformation from wgs84 to french NTF system, so
> between 2 different datum ( elipsoide)
> in gv sig it does not work. if you try manually the transformation, it
> will not work  because there are only parameters x y and z so it can be
> used for transformation in the same datum only . but in my case, 2 datum
> are different.
> it could work with epsg transformation ( all parametres are in epsg
> database) but when i choose epsg transformation in gvgis the box is
> empty.why ?
>
> this probleme of transformation will occured in all country when someone
> would like to translate gps data ( in wgs84) to his own projected system
> ( as ntf in france).
> i hope there will be a ansnwer from develloper team but the job is
> already so good that i don't want to bother them !!!
>
> thanks again ,
> Julien
>
> Sergio Clark a écrit :
> > Hello Julien,
> >
> > About your second question, I think it doesn't exist in the JCRS
> > extension an implemented transformation between 4326 and 27572 system.
> > So you can reproject your shapes but using "Without transformation"
> > option, and it's not as exact as using "EPSG transformation" option.
> > Maybe this is the error you see.
> >
> > You can also introduce manualy the Transformation parameteres ("Manual
> > Transformation" option), if you know them..
> >
> > Best regards,
> >
> > Sergio.
>
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-- 
Diego Guerrero Sevilla.

Instituto de Desarrollo Regional.
Universidad de Castilla-La Mancha.