[OSRS-PROJ] Projection of historic maps WW II - Italy

Clifford J Mugnier cjmce at lsu.edu
Fri Jun 6 12:29:53 EDT 2003


The Bessel 1841 parameters you listed are correct.  The Monte Mario Datum
of 1875 is not going to be significantly different from the current Monte
Mario Datum of 1940.  The Istituto Geografico Militare occasionally "lets
out" datum shift parameters from their national datum to WGS84, but the
parameters vary considerably from one region of Italy to another.  They are
the only RELIABLE source of such transformation parameters.

The projection parameters you list are correct, but the scale factor at
origin is 0.998992911

If you obtain some reliable datum shift parameters, please share them with
the list including your source and the area for which they are applicable.

Clifford J. Mugnier (cjmce at LSU.edu)
Chief of Geodesy
Center for GeoInformatics
Dept. of Civil Engineering
CEBA 3223A
Baton Rouge, LA  70810
Facsimiile (225) 578-8652
Voice       (225) 578-8536
Beep        (504) 382-4371

Dear List members,

I would appreciate assistance for the following problem:

Currently I try to define a map projection for a map from 1945,
Northern Italy. The map was made by the US Army Engr. Top. Co.
in Lambert Conic Orthomorphic. It is based on a map from 1931
done by Istituto Geografico Militare and was enhanced by aerial
photo surveys in 1944.

Given on the (scanned) paper map is:
- prime meridian Monte Mario (old!): 12d27'7.1E (in PROJ: 12d27'8.4E)
- "spheroid":     Bessel
- Origin:         14E, 45:54N
- False Easing:   800000 meters
- False Northing: 601000 meters
- The map provides the LCC grid and coordinates as well as
Lat/Long corners in reference to Monte Mario 12d27'7.1E (given as
"West from Rome" and Equator.

This projection I am defining in GRASS GIS which is based on the latest
PROJ from CVS. The parameters in GRASS style are (PROJ_INFO file)

name: Lambert Conformal Conic
towgs84: -104.1,-49.1,-9.9,0.971,-2.917,0.714,-11.68
proj: lcc
ellps: bessel
a: 6377397.1550000003
es: 0.0066743722
f: 299.1528128000
lat_1: 45.9
lon_0: 14.0000000000
x_0: 800000.0000000000
y_0: 601000.0000000000

The towgs84 parameter will be certainly wrong.

Using these values I achieve as accuracy a shift 70m eastwards and
170m northwards. For verification GIS data in Gauss-Boaga projection
from different providers were using (vector street map and orthophotos).
These maps I have reprojected into above LCC projection and compared to
the scanned and geocoded map from 1945:

For illustration there is a screenshot of a zoomed area:

To improve the accuracy, I am seeking assistance to find out:
- which Bessel definition should be used (is above right for these 1945
- which datum was used in 1945 (Italian or US or ...)
- how to define a different prime meridian: 12d27'7.1E instead of
(can I define a custom prime meridian?)

Thanks in advance

Markus Neteler
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