[Proj] Question about Italian conversion

[Oscar van Vlijmen]

> 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.