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

Romain Cherchi romain.cherchi at gmail.com
Fri Oct 6 11:28:23 EDT 2006

```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,

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 ?

\$ 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 ?