If some turning angles in the data are equal to pi, the corresponding pseudo-residuals
will not be included. Indeed, given that the turning angles are defined on (-pi,pi], an angle of pi
results in a pseudo-residual on +Inf (check Section 6.2 of reference for more information on the
computation of pseudo-residuals).
References
Zucchini, W. and MacDonald, I.L. 2009.
Hidden Markov Models for Time Series: An Introduction Using R.
Chapman & Hall (London).