[GRASSLIST:2326] Re: m.proj2

[Paul Kelly]

On Thu, 22 Jan 2004, Markus Neteler wrote:

> > > On Wed, Jan 21, 2004 at 02:10:38PM +0100, Ivan Marchesini wrote:
> > > > Dear Users,
> > > > I'm trying to use m.proj2 to translate a point from latlong ed50 coord sistem
> > > > to the italian sistem (gaus-boaga, rome40)
> > > > I have some difficulties to write the sintax of the command....
> > > > thank you...
> > >
> > > With 'cs2cs' (provided by PROJ4) it should be:
> > > LATLONG/ED50 -> Gauss-boaga Ovest/Roma40
> > >
> > > cat coordsED50.txt | cs2cs +init=epsg:4230 +to +init=epsg:26591 \
> > >       +towgs84=-85.88,-28.85,+49.67,-1.003,-2.383,-1.808,-27.82 > coordsGB1.txt
> > >
> > > Fuso Est:
> > >  Gauss-boaga Est is +to +init=epsg:26592
> > >
> > > Be sure to pick the right (local) towgs84 parameters.

Just realised Rome40 also uses the international ellipsoid. So you may not
need any datum transformation parameters at all in this simple example.

cs2cs +init=epsg:4230 +to +init=epsg:26591

should do the trick.
It would be good if there was a test point to check.
But anyway my other point was if neither datum is WGS84 then you need to
provided a set of towgs84 parameters for each side of the transformation
and then the calculation will go through WGS84 as an intermediate stage.

Paul