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

[Bud P. Bruegger]

Hi Gerald,

many thanks for responding.  Here some more information  (below)

On 29 Apr 2003 10:07:30 -0400
"Gerald I. Evenden" <gerald.evenden at verizon.net> wrote:

> The biggest problem for me is the lack of complete information.
> 
> 1. Italian IGM series? Old or new?  Are they based on UTM?

What the map states (translated from Italian) is the
following:

The kilometric grid is in the UTM system using the European Data
(Datum?) of 1950.  

It further states that the projection coordinates printed on the map
are UTM, zone 32, international ellipsoid.  


> 2. What are the specific geographic coordinates being projected
> 	and the x-y of the results.  What do you feel they should be?

The geographic coordinates printed on the map are relative to the
international ellipsoid "orientato"  (how do I translate this?) to (or
at?) Rome (Monte Mario).  (I suppose this is the prime meridian?)

The longitude of Rome, M.Mario is 12d 27' 08".04   

The longitudes printed on the map are "west of the meridian of Rome
(Monte Mario)".  

For the values that I expect, see below...

> 3. Correcting the longitude of Rome by hand?  Mighty big area to define
> 	by one point.

The longitude seems to be pre-defined in proj4, as, for example, in
-pm=rome.  So I thought the term "meridian of Rome" was defined.

> 4. The "PS" specification is incompleat and possibly redundant but
> 	Sorry, I can't read Italian so my "translation" may be
> 	suspect but there seems to be two central
> 	meridians.  

Yes, there are two zones (fuso in Italian), one West (Ovest in
Italian) and one East (Est in Italian) which use different central
meridians.  

> I would guess that "Ovest" and "Est" are west
> 	and east but no mention of north or south.  

Yes, for the zones.  So no need for north and south...

> Similarly, two
> 	false westings and eastings?  

Yes, referring to the two zones (West and East), respectively.

> The description seems incomplete.

What is missing?

> Lastly, the zone number of 32 is a little suspect and I would have
> chosen zone=33 which would put Roma closer to the central meridian.
> Lon 12 is the dividing line between zone 32 and 33.

I didn't mention that the map is of Tuscany, a little west of Rome...


Here the values that I expect:

for 1d 07' 30" west of the Rome Meridian (12d27'08".04) and 43d 0' 0"

the UTM coordinates should roughly be (read from a georeferenced
raster map) 

E=1689760.45  
N=4763707.54

Note that this is different from Gauss-Boaga.  The map actually prints
the Gauss-Boaga coordinates of that corner that are:

E=1689710
N=4763529

so some 200 meters off

I hope this defines the problem better.  Again, many thanks for your
help!

--b
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