//For all rotations in 2D (and a subset in 3D) calculate the pivot of this transformation
public static Vector3 calculatePivotPoint(Vector3 deltaPosition, Quaternion deltaRotation)
{
Vector3 axis; float angle; deltaRotation.ToAngleAxis(out angle, out axis);
Vector3 halfAngleDirection = Vector3.Cross(axis, deltaPosition);
Quaternion halfRotation = Quaternion.Slerp(Quaternion.identity, deltaRotation, 0.5f);
Ray preRay = new Ray(Vector3.zero, Quaternion.Inverse(halfRotation) * halfAngleDirection);
Ray postRay = new Ray(deltaPosition, halfRotation * halfAngleDirection);
return(Constraints.ClosestPointOnRayToRay(preRay, postRay));
}