Before revision: Agency Description Value (in meters) Ref IAU nominal "zero tide" equatorial IAU nominal "zero tide" polar IUGG equatorial radius IUGG semiminor axis (b) IUGG polar radius of curvature (c) IUGG mean radius (R1) IUGG radius of sphere of same surface (R2) IUGG radius of sphere of same volume (R3) IERS WGS-84 ellipsoid, semi-major axis (a) IERS WGS-84 ellipsoid, semi-minor axis (b) IERS WGS-84 ellipsoid, polar radius of curvature (c) IERS WGS-84 ellipsoid, Mean radius of semi-axes (R1) IERS WGS-84 ellipsoid, Radius of Sphere of Equal Area (R2) IERS WGS-84 ellipsoid, Radius of Sphere of Equal Volume (R3) GRS 80 semi-major axis (a) GRS 80 semi-minor axis (b) Spherical Earth Approx.
After revision: Agency Description Value (in meters) Ref IAU nominal "zero tide" equatorial IAU nominal "zero tide" polar IUGG equatorial radius IUGG semiminor axis (b) IUGG polar radius of curvature (c) IUGG mean radius (R1) IUGG radius of sphere of same surface (R2) IUGG radius of sphere of same volume (R3) NGA WGS-84 ellipsoid, semi-major axis (a) NGA WGS-84 ellipsoid, semi-minor axis (b) NGA WGS-84 ellipsoid, polar radius of curvature (c) NGA WGS-84 ellipsoid, Mean radius of semi-axes (R1) NGA WGS-84 ellipsoid, Radius of Sphere of Equal Area (R2) NGA WGS-84 ellipsoid, Radius of Sphere of Equal Volume (R3) GRS 80 semi-major axis (a) GRS 80 semi-minor axis (b) Spherical Earth Approx.