World Geodetic Datum 2000

Based on the current best estimates of fundamental geodetic parameters {W-0, GM, J(2), Omega} the form parameters of a Somigliana-Pizzetti level ellipsoid, namely the semi-major axis a and semi-minor axis b (or equivalently the linear eccentricity epsilon = root a(2) - b(2)) are computed and proposed as a new World Geodetic Datum 2000. There are six parameters namely the four fundamental geodetic parameters {W-0, GM, J(2), Omega} and the two form parameters {a, b} or {a, epsilon}, which determine the ellipsoidal reference gravity field of Somigliana-Pizzetti type constraint to two nonlinear condition equations. Their iterative solution leads to best estimates a = (6 378 136.572 +/- 0.053)m, b = (6 356 751.920 +/- 0.052)m, epsilon = (521 853.580 +/- 0.013)m for the tide-free geoide of reference and a = (6 378 136.602 +/- 0.053)m, b = (6 356 751.860 +/- 0.052)m, epsilon = (521 854.674 +/- 0.015)m for the zero-frequency tide geoid of reference. The best estimates of the form parameters of a Somigliana-Pizzetti level ellipsoid, {a,b}, differ significantly by -0.39 m, -0.454 m, respectively, from the data of the Geodetic Reference System 1980.