  We propose modeling an angle-of-arrival (AOA) positioning measurement as a
von Mises-Fisher (VMF) distributed unit vector instead of the conventional
normally distributed azimuth and elevation measurements. Describing the
2-dimensional AOA measurement with three numbers removes discontinuities and
reduces nonlinearity at the poles of the azimuth-elevation coordinate system.
Our computer simulations show that the proposed VMF measurement noise model
based filters outperform the normal distribution based algorithms in accuracy
in a scenario where close-to-pole measurements occur frequently.
