[Proj] Question about Italian conversion

[massimo at studiodemarchi.net]

Scrive Oscar van Vlijmen <ovv at hetnet.nl>:

> > From: Massimo De Marchi
> > Date: Mon, 24 Dec 2007 10:43:16 +0100
> > Subject: [Proj] Question about Italian conversion
> >
> > Hi,
> > I am a new user, and was performing image conversion with gdalwarp
> > between old Italian c.s. (Gauss Boaga) and WGS 84.
> >
> > I found there is a shift (around 100m)in the conversion. I tested with
> > cs2cs and I have the same issue.
> > The coordinate conversion is the same using both EPSG 3003 or 26591, or
> > using the proj4 string taken form spatialreference.org
> >
> > Starting with 1641163 East and 4997349 North I get
> > 10d47'40.422"E  45d6'52.824"
> > in place of:
> > 10d47'39.5"E    45d6'55.2"
> >
> > What am I doing wrong?
>
> Trying to follow the procedure with independent software, I get the
> impression that you didn't transform the datum from Hayford to WGS84.
> You simply inverse projected from x,y to lon,lat with the proper transverse
> mercator projection.
> With the Roma40 transform parameters found at <http://crs.bkg.bund.de>
> I arrive at lat,lon:
> 45d 06m 55.252s,  10d 47m 39.415s
> assuming a position vector rotation model (ISO) and an initial height of 0.
> The proj/epsg definitions you mention don't contain any datum transform
> instructions.
>
>

Thanks for your answer. I tried to do a coordinate transform using the -s_srs
EPSG:3003 (or 26591) and -t_srs EPSG:4326 parameters. How can I add the
necessary datum transform? I checked the documentation amd the forum, but
didn't find a clue.

Regards,
Massimo