[Proj] Italian Datum

[Mikael Rittri]

Hello Jan,
I would think it is EPSG:4806, "Monte Mario (Rome)". 
If you use 

   +init=epsg:4806

this would expand to 

+proj=longlat +ellps=intl +towgs84=-104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68 +pm=rome +no_defs  <>

(at least in Proj 4.8.0). The datum shift is intended for the
Italy mainland, and has accuracy 4 meters. There are other
published datum shifts designed for Sicily and Sardinia,
also with 4-meter accuracy, but if I recall correctly they
don't disagree by more than about 5 meters from the mainland
datum shift. 
    And there are several datum shifts for offshore areas 
around Italy; I haven't compared them with the mainland 
datum shift.

For a map in scale 1:100000, I think the mainland datum shift
should be okay for the entire Monte Mario area. 

Off-topic: Since about Christmas, I only get a small random 
subset of the Proj mails to my e-mail account. I don't
think it is due to my spam filter or wrong subscription
settings.
    Am I the only one with this problem?

Best regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

-------- Original Message ---------
Jan Hartmann j.l.h.hartmann at uva.nl 
Fri Jan 25 06:49:24 EST 2013 
________________________________________
Hi all,

I'm indexing an Italian map series 1:100.000, published around 1950 on 
the basis of measurements in the first half of the 20th century. Map 
sheets are registered in lat-lon values, 30 seconds east-west 20 seconds 
north east, with Rome as central meridian (12d27'08''40). Those values 
are on the International Ellipsoid. I would like to transform those 
values to WGS84. In the Proj4 epsg file I find lots of latlon 
projections with ellps=intl and different +towgs84 parameters. I read 
Cliff Mugnier's column about Italy 
(http://www.asprs.org/a/resources/grids/08-2005-italy.pdf), but I am 
unable to find which epsg number is most appropriate for these maps. Can 
anyone help?

Jan