def same_direction?(rhs)
      Util3D.check_arg_type(Vector3, rhs)
      return false if(!parallel?(rhs))
      return false if(self.dot(rhs) < self.tolerance)
      return true
    end
def same_direction?(rhs)
      Util3D.check_arg_type(Vector3, rhs)
      return false if(!parallel?(rhs))
      return false if(self.dot(rhs) < self.tolerance)
      return true
    end
[Input]
  _rhs_ should be Vector3.
 [Output]
  return true if myself and rhs have same direction as boolean.