1. An apparatus-based method for calibration of a three-dimensional (3D) field sensor, comprising: accessing a plurality of samples, the samples from the 3D field sensor, each sample representing a magnitude and an orientation of a 3D field sensed by the 3D field sensor; using the plurality of samples, determining a plurality of parameters of an ellipsoid, wherein the determining the plurality of parameters is performed so that the ellipsoid fits the plurality of samples, wherein the following is used to represent the ellipsoid: x 2 +y 2 +z 2 −U(x 2 +y 2 −2z 2 )−V(x 2 −2y 2 +z 2 )−4Mxy−2Nxz−2Pyz−Qx−Ry−Sz−T=0, and wherein determining a plurality of parameters determines the parameters {right arrow over (s)} LS =(U,V,M,N,P,Q,R,S,T) T ; determining a transformation that transforms the ellipsoid into a sphere; applying the transformation to a sample to create a transformed sample; and using the transformed sample to determine at least an orientation of the apparatus.