What's the mathmatics formula in robot_localization

edit

You can read this paper from the authors of the package. But even there it's a bit unclear what the exact state update is. This question contains some details too.

As I understand it they assume a second order model for all calculations and estimate the velocity+acceleration from measurements, they then use the standard EKF update. But I haven't been able to find details on how these motion model parameters are estimated.