[GRASSLIST:8230] Re: Gauss-Boaga location and wgs84 proj parameter

[Paul Kelly]

Hello Luca and Clifford

On Fri, 9 Sep 2005, Luca wrote:

 > Im going to create a Gauss-Boaga location where to load some 
georeferenced
 > maps. This is what I have done:
 >
 > *1.*
 >

 > What is the right number? i would think that is the /*1st*/ (couse im 
in the
 > north of Italy) or the /*4th*/

Either will do but the former will probably be more accurate.

 > How can i know which towgs84 parameter have i to use?

It is generally determined by the area covered by your map and the level 
of accuracy you desire.

 > and.. if the right parameter is the first, why is there the 4th 
parameter,
 > that is so strange?

To put it simply, the first one covers the area described (peninsular 
Italy) with relatively high accuracy. The fourth covers the entire area 
the Rome 1940 datum is used in (including islands) with lower accuracy.


On Fri, 9 Sep 2005, Clifford J Mugnier wrote:

 > Luca,
 >
 > None of those are correct.  What you have listed are the datum shift
 > parameters between European Datum 1950 and the WGS 84 datum.

I'm not sure about that: I am maintaining that part of GRASS and put the 
parameters there based on the information at this website: 
http://crs.bkg.bund.de/crseu/crs/eu-countrysel.php?country=IT

As far as I can see are they not the same as those given in the last 
paragraph of the August 2005 PE&RS article? (I couldn't find it on the 
website but am a member of ASPRS so I have a paper copy :) )

Paul