def distance(cls, q0, q1):
        """Quaternion intrinsic distance.

        Find the intrinsic geodesic distance between q0 and q1.

        Params:
            q0: the first quaternion
            q1: the second quaternion

        Returns:
           A positive amount corresponding to the length of the geodesic arc
           connecting q0 to q1.

        Note:
           Although the q0^(-1)*q1 != q1^(-1)*q0, the length of the path joining
           them is given by the logarithm of those product quaternions, the norm
           of which is the same.
        """
        q = Quaternion.log_map(q0, q1)
        return q.norm