[Gdal-dev] AAIGrid driver: small PROJCS detection problem

[Markus Neteler]

On Mon, Apr 19, 2004 at 03:31:08PM -0400, Frank Warmerdam wrote:
> Markus Neteler wrote:
> 
> >The PROJCS is set "unnamed", shouldn't it be Transverse_Mercator
> >or is the problem related to the fact that the projection is
> >very particular? It should be the Italian Gauss-Boaga, but
> >the modified version from the Province of Bolzano. Note the
> >Xshift        -1000000.0000000000
> >Yshift        -5000000.0000000000
> >
> >which is probably ignored (the center should be around
> >Center Longitude: 11:25:49.77287E [11.43049]
> >Center latitude:  46:39:01.079651N [46.65030]
> >).
> >
> >So maybe there are two problems?
> 
> Markus,
> 
> The fact that the PROJCS is "unnamed" is fine.  If there was
> a way to know a meaningful user name for the coordinate system
> it would be nice to substitute it, but that is tricky.
> 
> I see two issues.
>  1) The Spheroid (INTERNATIONAL1909) was not recognised, so WGS84
>     was incorrected used as a default.  I have committed a small change
>     to recognise INTERNATIONAL1909 in CVS.

Thanks - this was the most important part.

>  2) The Xshift/Yshift were ignored.  I don't really understand the
>     semantics though so I am not sure what to change.
> 
> If you know what should be done for the X/Y shift values, I would
> suggest you submit a bug report.

I have got/patched the WKT definition:

 PROJCS["Monte_Mario_Italy_1_BZ",
    GEOGCS["GCS_Monte_Mario",
        DATUM["Monte_Mario",
            SPHEROID["International_1924",6378388,297]],
        PRIMEM["Greenwich",0],
        UNIT["Degree",0.017453292519943295]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["False_Easting",500000.0],
    PARAMETER["False_Northing",-5000000.0],
    PARAMETER["Central_Meridian",9],
    PARAMETER["Scale_Factor",0.9996],
    PARAMETER["Latitude_Of_Origin",0],
    UNIT["Meter",1]]

Changes:
 PROJCS: _BZ I have added
 False_Easting: -1 million to reduce coordinates by 1 digit
 False_Northing -5 million to reduce coordinates by 1 digit

These are data from the local government. In the 80th they
had decided to implement this particular False_Easting, 
False_Northing...

I have applied above to gdal_translate with '-a_srs bz_wkt.txt'
to receive a GeoTIFF from the original ASCII DEM,
but it was reduced to a WGS84 ellipsoid.
Is it not possible to generate data with user defined
WKT definitions? Maybe that's not desired - but then
I'm limited to what EPSG provides (where above definition
doesn't exist).

Best regards

 Markus Neteler