[Proj] Lambert Conformal Conic

[Cuinet Jérôme]

With both Lambert 93 and 9 Lambert CC, the ellipsoid used is the GRS80 (wich 
is similar to WGS84), the precision is the same. The one difference is the 
scale factor on the application area. The geodetic datum is named RGF93 
(réseau géodésique français).

For Lambert II Étendu, the geodetic datum has always been NTF. There are no 
changement, and I think that datum or based grid is as important as 
ellipsoid specification.

Jérôme Cuinet

----- Original Message ----- 
From: "Irwin Scollar" <al001 at uni-koeln.de>
To: <proj at lists.maptools.org>
Sent: Sunday, April 26, 2009 11:14 AM
Subject: [Proj] Lambert Conformal Conic

Today, three variants are supported by IGN, one
using a WGS84 ellipsoid covering the whole of the
country called Lambert 93, one using the Clarke
1880 ellipsoid like the old NTF based grid did,
with the dual latitudes of the old NTF zone II
and a different false Northing called Lambert
Extended II, and one for higher precision using 9
zones and the GRS80/WGS84 ellipsoid called
Lambert CC (Coniques Conformes).  Lambert 93 is
now the standard for most products from the IGN.

Irwin Scollar