I do not know the answer nor do I think there is a simple answer, but if you refer to the following excellent textbooks and recreate their illustrations, you will likely get the answer and much more.
1. Brown, R. G. and Hwang, P. Y. C., Intro. to Random Signals and Applied Kalman Filtering, 4th ed, John Wiley 2012, Sec. 7.5
2. Gibbs, B. P., Advanced Kalman Filtering, Least-Squares and Modeling, Wiley 2011, Sec. 11.7
3. Crassidis, J. L., and Junkins, J. L., Optimal Estimation of Dynamic Systems, 2nd ed, CRC Press 2012, Sec. 3.7
4. Ristic, B., Arulampalam, S., and Gordon, N., Beyond the Kalman Filter, Artech House 2004
These references should suffice to begin with. I am at IIT Indore. For further communication, please contact me at [email protected].