1. Chen, D., Menegatto, V.A., Sun, X.: A necessary and sufficient condition for strictly positive definite functions on spheres. Proc. Amer. Math. Soc. 131, 2733–2740 (2003)
2. NASA.: The NASA GSFC and NIMA Joint Geopotential Model. http://cddis.gsfc.nasa.gov/926/egm96/ (1998)
3. Fasshauer, G.E., Schumaker, L.L.: Scattered data fitting on the sphere. In: Daehlen, M., Lyche, T., Schumaker, L.L. (eds.) Mathematical Methods for Curves and Surfaces II, pp. 117–166. Vanderbilt University Press, Nashville, TN (1998)
4. Freeden, W.: On spherical spline interpolation and approximation. Math. Methods Appl. Sci. 3, 551–575 (1981)
5. Freeden, W., Gervens, T., Schreiner, M.: Constructive Approximation on the Sphere (With Applications to Geomathematics). Oxford Science (Clarendon), Oxford, UK (1998)