Issues in the description of the nearly-constant turn rate model

[narykov]

The description of the nearly-constant turn rate model in here doesn't look right.

The expression of $F(x)$ here is a vector, not a matrix as implied by $F$. An appropriate $F$ matrix can be seen, e.g., on p. 16 in here, but a bit struggling with finding a good reference. Regardless, in the entries to this vector above, it should be $x_{pos}$, not just $x$ (and the same, respectively, for $y$). Finally, a bit surprised to see $q_{\omega}^2$ not scaled by the time interval, which seems contradictory to the SDE in the model's description that states $d\omega = q_\omega dt$.

[narykov]

OK, found a semi-decent conference paper with Bar-Shalom among the authors, which exposes the $F$ and $Q$ matrices. Indeed, the element in $Q$ that describes the turn rate noise is time-dependent, which means that the following is brought into question, i.e., q**2 may need to be turned into dt * q**2:

Stone-Soup/stonesoup/models/transition/nonlinear.py

Lines 132 to 134 in ddb5172

	Q = np.array([[dt**3 / 3., dt**2 / 2.],
	[dt**2 / 2., dt]])
	C = block_diag(Q*q_x**2, Q*q_y**2, q**2)

P.S. It would be good to find reference for q**2, since in the publications I've come across either $q$ or $\sigma^2$, but never $q^2$.

[narykov]

Just a small thing, there is no dependency on $x$ in $F(\cdot)$ below:

Thanks!