A. A. Ardalan - Department of Surveying and Geomatics Engineering, University of Tehran, P.O. Box ۱۱۳۶۵-۴۵۶۳, Tehran Iran,
E. W. Grafarend - Department of Geodesy and Geoinformatics, Stuttgart University, Geschwister-Scholl-Str. ۲۴ D, D-۷۰۱۷۴,Stuttgart Germany,

Four fundamental geodetic parameters, namely 0 2 { , GM W,Ω,J}, determine a world geodetic datum. With respect to the Somigliana-Pizzetti Level Ellipsoid / International Reference Ellipsoid these fundamental parameters from best estimates at a reference epoch determine its semi-major axis a as well as its semi-minor axis b (or equivalently the linear eccentricity ε = a2−b2). Satellite orbit analysis as well as sea level projects have indicated that the four fundamental geodetic parameters are time-dependent, described for instance by 0 {(GM)!,W! 2 , , } J Ω! ! . Here we have 0 {(GM)!,W! ,Ω! 2 ,J! }. Here we have analyzed the impact of best estimates of 0 2 {W! ,J!} on shape and size parameters, i.e., {a!,b!} and {a!,ε!}, of the World Geodetic Datum 2000 (WGD2000). Based on the best estimate of time variations of 0 2 {W! ,J!} we have computed the best estimates a! = (0.3 ± 0.02) mm/year , b! = (−0.0002 ± 0.00008) mm/year , and ε! = (3.7 ± 0.3) mm/year as the time variation of the shape and size parameters of the WGD 2000. The new results give a scientific basis for answering the question: Is there a need for a Geodetic Datum 2000?

World Geodetic Datum 2000 (WGD 2000), four fundamental geodetic parameters, Somigliana-Pizzeti Level Ellipsoid