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Transformation from Gauss-Boaga to WGS84   Oktawian Ewiak Feb 23, 2006
Re: Transformation from Gauss-Boaga to WGS8...   Melita Kennedy Feb 25, 2006
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Subject Transformation from Gauss-Boaga to WGS84 
Author Oktawian Ewiak 
Date Feb 23, 2006 
Message I have a problem with a projection transformation.

The data (shapefiles:.shp,.shx & .dbf) is in Gauss-Boaga with datum Rome 1940. I need to transform it into UTM Zone 32N/WGS84.
I tried the Projection Utility Wizard in Arcview3.2 :

First I had to set the projection, because it was set to "unknown", so i chose "Monte_Mario_Rome_Italy_1 [26591]". Then in step 3 I chose "WGS_1984_UTM_Zone_32N [32632]" as the new coordinate system.
Then I got the message that the coordinante systems specify different datums. As far as I know "Monte_Mario_Rome" uses Rome1940.

How can I change the datum from Rome1940 to WGS84? I see an option to transform from Monte_Mario_Rome to Monte_Mario, also from Monte_Mario to WGS84, but no option for a transformation from Monte_Mario_Rome to WGS84...

Can anybody help? I am a beginner. Maybe I have overseen something.

Edit:
I have some additional data which is in WGS_1984_UTM_Zone_32N and which I use to check if I made a mistake.
It seems that the data for my map is now in WGS_1984_UTM_Zone_32N, but still refers to the datum Monte_Mario.
The East-West coordinates (Easting) are fitting good, but the North-South coordinates have an offset of around 250m.
What is the difference between Monte_Mario and WGS84? 
   
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Subject Re: Transformation from Gauss-Boaga to WGS84 
Author Melita Kennedy 
Date Feb 25, 2006 
Message Hi,

When you set up the input coordinate system, see if you can find Monte_Mario_Italy_1. The one you used assumes that the geographic coordsys and projection parameters are relative to the Rome prime meridian (origin of longitude values) rather than Greenwich. So, "GCS_Monte_Mario_Rome" has a prime meridian set to Rome, while "GCS_Monte_Mario" is using the Greenwich prime meridian. The transformations will be similar (look for Monte_Mario, not Monte_Mario_Rome.

Even so, you should be able to set two transformations (monte mario rome to monte mario, then monte mario to wgs84) if you set one on step 2 and step 3. However, you have to go to step 3 to set the output coordinate system, then go back to step 2 to set the first transformation (monte mario rome to monte mario).

Melita 
  Melita Kennedy
ESRI Product Specialist