This returns the third flattening given an eccentricity.
Examples:
Scalar input:
e_earth = 0.081819221456; n_earth = ecc2n (e_earth) => n_earth = 0.0016792
Vector input:
e_vec = [ 0.081819221456 0.3543164 ] n = ecc2n (e_vec) => n = 0.0016792 0.033525
See also: n2ecc.
Package: mapping