Show "Quaternion Cubic Spline" (i.e. "natural")

[mgeier]

See https://qspline.sourceforge.net/ and especially https://qspline.sourceforge.net/qspline.pdf

James McEnnan (2003), "Quaternion Cubic Spline"

[mgeier]

Something like this seems to be implemented in https://docs.scipy.org/doc/scipy/reference/generated/scipy.spatial.transform.RotationSpline.html

However, they refer to a derivation based on rotation matrices instead of quaternions: https://github.com/scipy/scipy/files/2932755/attitude_interpolation.pdf