[OSRS-PROJ] Older Stateplane Definitions

[Paul Ramsey]

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.
What is the nicest way to properly represent the gradian projections in
proj4 syntax? A quick hack would be to directly convert the angular
units in the projection definition from gradians-paris to
degrees-greenwich. That would still leave open the problem of how to
convert into gradians in geographic.

P.

Craig Bruce wrote:
> 
> The definitions of the following coordinate systems are incorrect:
> 
> # Nord_de_Guerre <27500>
> # NTF_Paris_France_I <27581>
> # NTF_Paris_France_II <27582>
> # NTF_Paris_France_III <27583>
> # NTF_Paris_France_IV <27584>
> # NTF_Paris_Nord_France <27591>
> # NTF_Paris_Centre_France <27592>
> # NTF_Paris_Sud_France <27593>
> # NTF_Paris_Corse <27594>
> 
> As indicated previously, they are incorrect because the angluar parameters
> are actually in Gradians relative to the Paris Prime Meridian but PROJ will
> assume that they are in Degrees relative to the Greenwich Prime Meridian.
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