Calculates the angle (in radians) of the rotation taking one orientation to another.
Two orientation objects
y is missing in a call to
it is treated as the identity, i.e.
rotation.angle(x) is calculated.
rotation.distance returns a vector of length
angle of the rotation taking corresponding elements of
y (with the
usual recycling rules if they are different lengths).
rotation.angle is equivalent to calculating the
rotation.distance to the