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

Tue Apr 29 13:20:59 EDT 2003

Thanks, Clifford, for answering.  I don't believe that the projection
of the map I'm working with (possibly as opposed to what I stated in
the PS. of my post).  is Gauss-Boaga, however.  At least the grid
printed on the map is stated to be UTM, zone 32, international
ellipsoid and European Datum of 1950.  While the longitudes printed on
the map are west of Rome (M.Mario), that should not affect the
projection (unless I misunderstand something here).   

Actually, the map prints the Gauss-Boaga coordinates of the map
corners and they seem to differ from the desired UTM coordinates in
the range of about 200 meters.  (For numbers, see my other response to
the list).  

All this applies to my actual problem with an old series 1:25000 IGM
(the Italian mapping agency) map.  What you said may well apply to the
more detailed data that I listed in the P.S. of my post.  (Although
I didn't think so--but obviously I must go wrong somewhere...).

many thanks and I hope the additional information in the other reply
to the list allows to find a solution!

cheers
--bud

On Tue, 29 Apr 2003 10:38:49 -0500
"Clifford J Mugnier" <cjmce at lsu.edu> wrote:

> 
> The systems being referred to are the old Gauss-Boaga Transverse Mercator
> Grid and it is based on the Monte Mario Datum of 1940.  Rome is the Prime
> Meridian from whence the two zones are measured.  The scale factor at
> origin is 0.9996, but is NOT UTM.  Furthermore, it is oft confused with the
> military system used in Italy as specified by NATO which is European Datum
> of 1950 with UTM measured from Greenwich.  The latitudes and longitudes are
> different - different datums in addition to the grids.
> 
> Gauss-Boaga is a specific truncation and has characteristic distortion that
> is masked by inadvertent substitution with Gauss-Kruger.  For
> survey-quality work it DOES make a difference.  For 1:50,000-scale GIS work
> it does not make a difference on land - it does offshore.
> 
> The datum shift generally quoted is that found in the NIMA TR 8350.2 (WGS84
> Datum) which is ONLY for EU50 to WGS84.  The derivative EPSG database gives
> no further guidance.  On occasion the Istituto Geografico Militare in
> Firenze (Florence) will give out a 7-parameter transformation for a local
> area of Italy, but be careful as they use left-handed rotations.
> 
> Most cadastral mapping is still based on the aphylactic Cassini-Soldner
> Grids.  Italy has only 540 of them.
> 
> So now you know.
> 
> Cliff Mugnier
> LOUISIANA STATE UNIVERSITY
> 
> The biggest problem for me is the lack of complete information.
> 
> 1. Italian IGM series? Old or new?  Are they based on UTM?
> 
> 2. What are the specific geographic coordinates being projected
> and the x-y of the results.  What do you feel they should be?
> 
> 3. Correcting the longitude of Rome by hand?  Mighty big area to define
> by one point.
> 
> 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.  I would guess that "Ovest" and "Est" are west
> and east but no mention of north or south.  Similarly, two
> false westings and eastings?  The description seems incomplete.
> 
> 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.
> 
> The following script:
> ./lproj +proj=utm +zone=32 +ellps=intl <<EOF
> 12d37E 41d52N
> EOF
> ./lproj +proj=utm +zone=33 +ellps=intl <<EOF
> 12d37E 41d52N
> EOF
> 
> produces the results:
> 
> 800183.96       4641382.04
> 302191.13       4637801.10
> 
> On Tue, 2003-04-29 at 03:45, Bud P. Bruegger wrote:
> > Hello everyone,
> >
> > I hope someone can help me with what should probably be an easy
> > question.
> >
> > For an old series Italian IGM 1:25,000 map, I try to project the map
> > corners (whose lat/long is known) to UTM (as used in the map).
> >
> > I naively tried the following:
> >
> > proj +proj=utm +zone=32 +ellps=intl
> >
> > and corrected the longitude by hand for the meridian of Rome
> > (12d27'8.4"E).  But the UTM coordinates that come out don't seem to
> > be correct.  Any idea what I'm doing wrong and how the projection
> > should be defined?
> >
> > Also, if anyone has a numeric example handy for testing...
> >
> > Many thanks for any help I can get!
> >
> > --bud
> >
> > PS.  I found the following information that is probably for the new
> > series IGM that may shed more light on my problem:
> >
> >  Transverse_Mercator (ARC/INFO keyword: TRANSVERSE)
> >  Unità di Distanza Planare: METRI (ARC/INFO keyword: METERS)
> >  Fattore di scala al meridiano centrale: 0.99960
> >  Longitudine del meridiano centrale: -3°27'08.4'' per il fuso Ovest /
> >                                      +2°32'51.6'' per il fuso Est
> >  Falso est: 1500000 per il fuso Ovest /
> >             2520000 per il fuso Est
> >  Nome del Datum: MOD
> >  Nome dell'Ellissoide: INTERNATIONAL1909
> >
> >
> > /-----------------------------------------------------------------
> > | Bud P. Bruegger, Ph.D.
> > | Sistema (www.sistema.it)
> > | Via U. Bassi, 54
> > | 58100 Grosseto, Italy
> > | +39-0564-411682 (voice and fax)
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| Sistema (www.sistema.it)
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