[OSRS-PROJ] Older Stateplane Definitions ???

[Gerald Evenden]

Paul Ramsey wrote:

> Interesting. Learn something new every day. For the benefit of all, here
> is the ESRI WTK definition of NTF_Paris_France_I <27581>
>
> PROJCS[
>   "NTF_Paris_France_I",
>   GEOGCS["GCS_NTF_Paris",
>     DATUM["D_NTF",
>       SPHEROID["Clarke_1880_IGN",6378249.2,293.46602]
>     ],
>     PRIMEM["Paris",2.337229166666667],
>     UNIT["Grad",0.015707963267948967]
>   ],
>   PROJECTION["Lambert_Conformal_Conic"],
>   PARAMETER["False_Easting",600000],
>   PARAMETER["False_Northing",1200000],
>   PARAMETER["Central_Meridian",0],
>   PARAMETER["Standard_Parallel_1",55],
>   PARAMETER["Scale_Factor",0.999877341],
>   PARAMETER["Latitude_Of_Origin",55],
>   UNIT["Meter",1]
> ]
>
> Here is the definition I got from OGR converting from WKT to Proj4:
>
>   +proj=lcc
>   +lat_1=55.000000000
>   +lat_2=0.000000000
>   +lat_0=55.000000000
>   +lon_0=0.000000000
>   +x_0=600000.000
>   +y_0=1200000.000
>   +a=6378249.200
>   +b=6356515.000
>   +units=m
>
> As noted, there is no flag that the angular units are gradians-paris, so
> they'll be misinterpretted as degrees-greenwich.

    ...

All longitude is from the geographic coordinate origin which is not
explicitly defined.  So it can just as well be relative to the French origin.
The later, proj, definitioin is not in error unless one assumes that the
Greenwich origin is used.

To use Greenwich data with proj one can merge the 2.33 correction into
the lon_0 factor.

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