The method described looks similar to [0] which extends Euclidean spline curves to Lie groups using the exponential map (here the conversion from/to scaled-angle-axis)<p>[0]: A general construction scheme for unit quaternion curves with simple high order derivatives <a href="https://dl.acm.org/doi/10.1145/218380.218486" rel="nofollow">https://dl.acm.org/doi/10.1145/218380.218486</a>