A Possible Intuitive Derivation of the Kerr Metric in Orthogonal Form   Based On Ellipsoidal Metric Ansatz
  In this paper we show that it is possible to derive the Kerr solution in an alternative, intuitive way, based on physical reasoning and starting from an orthogonal metric ansatz having manifest ellipsoidal space-time symmetry (ellipsoidal symmetry). This is possible because both flat metric in oblate spheroidal (ellipsoidal) coordinates and Kerr metric in Boyer-Lindquist coordinates can be rewritten in such a form that the difference between the two is only in the time-time and radial-radial metric tensor components, just as is the case with Schwarzschild metric and flat metric in spherical coordinates. 
Branislav D. Nikoli\'c, Milan R. Panti\'c
gr-qc