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

[Bud P. Bruegger]

Hi Gerald,

Adding Gauss-Boaga may be a nice thing.  I'm not a specialist of
Italian projections (I'm really doing this to sort something out for
my wife and haven't done any GIS work in Italy for years).  

The best info I found to check on how Gauss-Boaga works is probably
with the Geographic Transformation Engine project
(http://www.mondogis.it/open/gte/doc/gteinfo.html).  They have some
sample scripts to convert from Gauss-Boaga to UTM (bottom of
http://www.mondogis.it/open/gte/doc/gtescript.html) but the links seem
to be broken. ....fixing links.....downloading....

The following GTE script converts from geographic coordinates on WGS84
to Gauss-Boaga zone West:  WGS84-GBO.xml  (attached)

I hope this is useful to confirm that what you found below is correct.  

I'll try to get hold of an article that describes the Italian
georeferencing systems better--but that may take some days to
materialize...

best cheers
--bud


On 29 Apr 2003 14:21:33 -0400
"Gerald I. Evenden" <gerald.evenden at verizon.net> wrote:

> The variety of names for the Transverse Mercator projection creates
> a hideous problem.  Are the names merely nationalistic pride or do
> they merely represent different datums/prime-meridians or are they
> computationally different?  From my point of view I am only concerned
> about how they are computed and leave datums/prim-meridians to others.
> 
> +tmerc in the libproj library uses the equation set based upon
> Thomas' "Conformal Projections ..." page 97.  This version has a
> few more terms than Snyder's Working Manual, page 61. I take it that
> the Boaga-Gauss has elided a few more terms.
> 
> The question now becomes should I add another version of tmerc
> with the truncated evaluation similar to what was done with the
> French version of the conformal conic?  And call this the "boaga"
> projection?
> 
> The following is copied from
> http://remotesensing.org/geotiff/proj_list/transverse_mercator.html
> and is basically a copy of Snyder's version.
> Easting, E =  FE + k0*[A + (1 - T + C)A3/6 + (5 - 18T + T2 + 72C -
> 	58e'2)A5/120]	
> Northing, N =  FN + k0{M - M0 + *tan*[A2/2 + (5 - T + 9C + 4C2)A4/24 + 
> 	(61 - 58T + T2 + 600C - 330e'2)A6/720]}
> This is lumped with other discussions that include the Boaga projection
> and thus implying that it defines the Boaga projection.
> 
> Is this true??
> 
> Thank-you from confused on Cape Cod.
> 
> On Tue, 2003-04-29 at 11:38, Clifford J Mugnier wrote:
> 	...
> > 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.
> 
> 
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| Bud P. Bruegger, Ph.D. 
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