[Proj] What projections arguments to specify a custom ellipsoid ?

[Romain Cherchi]

Hello,

I'm trying to add a line in the PostGIS SPATIAL_REF_SYS Table.

My SRS WKT is:
PROJCS["NTF_Lambert_II_étendu",
    GEOGCS["GCS_NTF",
        DATUM["Nouvelle_Triangulation_Francaise",
            SPHEROID["Clarke_1880_IGN",6378249.2,293.46602]],
        PRIMEM["Greenwich",0.0],
        UNIT["Degree",0.0174532925199433]],
    PROJECTION["Lambert_Conformal_Conic_1SP"],
    PARAMETER["False_Easting",600000.0],
    PARAMETER["False_Northing",2200000.0],
    PARAMETER["Central_Meridian",2.3372291667],
    PARAMETER["Standard_Parallel_1",45.8989188889],
    PARAMETER["Standard_Parallel_2",47.6960144444],
    PARAMETER["Scale_Factor",1.0],
    PARAMETER["Latitude_Of_Origin",46.8],
    UNIT["Meter",1.0]]

And I'm trying to figure out what is the corresponding proj4text:
+proj=lcc    +x_0=600000
                  +y_0=2200000
                  +lon_0=2.3372291667
                  +lat_1=45.8989188889
                  +lat_2=47.6960144444
                  +k_0=1
                  +lat_0=46.8
                  +units=m
                  +a=6378249.2
                  +towgs84=-168,-60,320,0,0,0,0
                  +pm=greenwich

However, I've some problems finding information about projections arguments,
especially about spheroid information.

SPHEROID["Clarke_1880_IGN",6378249.2,293.46602]],

I guess I can use "+a" for 6378249.2 but what is  the argument for
293.46602 ?

NB: I already tryied :
$ proj -le | grep clrk80
   clrk80 a=6378249.145    rf=293.4663      Clarke 1880 mod.

But it seam that I can't use the +ellps=clrk80 because the values don't
match exactly with mine.

May I use +rf=293.46602 ?

What about this UNIT["Degree",0.0174532925199433]], ?



Thanks in advance


Best regards
-- 
Romain CHERCHI
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