[Proj] [OSRS-PROJ] Projection parameters for Italian old IGM?

[Oscar van Vlijmen]

> From: "Luca Lastrucci" <luca.lastrucci at powersoft.it>

> I found your message on the newsgroup about conversion from Gauss-Boaga to
> WGS84 for Italy.
> Because I'm developing a tool and I have the same problem, can you suggest me
> a .dll, .ocx,... or source code, to do that?

Probably nearly everything that can be said about Gauss-Boaga can be found
in the lists.maptools - PROJ archives.
If you can do datumshifts, then you can convert from the Hayford / ED50
ellipsoid to WGS84. See for the transform params for both Italian zones
http://crs.bkg.bund.de/crs-eu
If you can do a transverse Mercator projection, then you can do Gauss-Boaga.
Taking a place far from a central longitude, for instance a location around
Otranto: 40d 09m N 18d 30m E in Fuso 2, I get a difference of around 120
microns in the longitude and only a couple of microns in the latitude.
I used the Gauss-Boaga formulae in the Libproj4 manual, page 42.
Something to take note of: in Gauss-Boaga longitudes are usually with
respect to Monte Mario at 12d 27m 08.4s E.