How to manage the South Italy projection with ArcGis and QGis.

The reference website for coordinate systems
used
during World War II is Thierry Arsicaud’s website
: Notes on the “Modified
British System” used on the European Theatre of Operations during the
WWII.

In
1919, Great Britain adopted in its territory the “British System”,
based on a Cassini-type map projection and the use of a
grid designed to facilitate the reading of the coordinates of the designated
points . This system was replaced
in
1927 by the “ British Modified System”, more
suited to cover large geographical areas and military operational use by
land  or airlift
forces.
This
“British Modified” system was used during the second world war
by the British and American armies by being
extended
to European, North African, the Near East and South East Asian operation
theatres.

The following figure , from
Thierry Arsicaud’s website shows
the areas corresponding to the projections in course
during
World War II.   

The South Italy projection is a secant Lambert
projection ( only one standard parallel), which
uses the ellipsoid Bessel 1847.

The South Italy projection
management with ArcGIS

You will not find this projection in those available
as
standard with ArcGis.
Once
the projection is created, it will be necessary to enter the
transformation methods to the usual systems (WGS84, NTF, RGF93).

The parameters of the South Italy projection are the
following:

False_Easting 700000.0
False_Northing
600000.0
Central_Meridian
14 E
Standard_Parallel_1
39 , 5 ° N
Scale_Factor
0.99906

In terms of the geodesic system, the parameters
are
:

Name: Bessel 1841
Angular
Unit: Degrees
Prime
Meridian: Greenwich
Datum:
D_Bessel_1841
Spheroid:
Bessel 1841
Semimajor
Axis: 6377397.155
Semiminor
Axis: 6356078.963
Inverse
Flattening: 299.1521535
Click
on the following link to download a file .
prj with all the necessary definitions.

[ dg ids = “2428”]

To move this projection to
the data block or to
a GIS layer, open the coordinate systems definition window
and click on the import button:   

How to set up
transformations
in ArcMap

The transformation of Bessel datum 1841 to NTF or RGF93 is
done through a three- parameter
transformation dX , dY, dZ .

The values to go from Bessel to NTF are :

dX = 850,

dY = -143 and

dZ = 160

The values to change from Bessel to RGF93 or WGS84 are :

dX = 682,

dY = -203 and

dZ = 480

To set up the transformation of this geodesic system towards the
one you usually use :

1-Open a new project in ArcMap
2-Load
a layer in the usual projection
system (Lambert 93 or Lambert I , II, II, IV , or extended II )
3-Load
a map in South Italy projection

You will notice that a window
appears, indicating you that the geodetic systems are different and
which proposes you to set up a transformation.

4-Click the Transformations button If you are working with Lambert I, II, II, IV or II extended

5-Make
sure that in Convertlater  you
have
Bessel_1841
6-That
in To , you have well
GCS_NTF
7-Click
on New

8- In Name type Bessel_NTF

9-In
settings enter the values 850, -143 and 160
for, respectively, X, Y, Z.
10-Click
OK , and OK

Next time you have to perform a transformation, you
will find this transformation in the drop
down list.

The management of the South Italy
projection
with QGis

Similarly as with QGis, the transformations are
performed
automatically
(provided that you inform the ellipsoids ), it
is
much simpler to manage this projection than with
ArcGis.

To define a new coordinate system
Custom
, click the Preferences menu ->CustomProjection

In Name enter
South Italy

In settings enter
the proj4 definition of the projection:

+ proj =
lcc
+
lat_0 = 39.5 + lat_1 = 39.5 + lon_0 = 14 + k_0 = 0.99906 + x_0 = 700000 + y_0 =
600000
+
ellps
=
bessel
+
units = m + no_defs

Click OK.
And,
now you can work with the South Italy projection
and overlay data in this
projection with data depicting other projections.

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