code: def camera_position(self, pose=None):
          '''
          returns camera position in world coordinates using self.rvec and self.tvec
          from http://stackoverflow.com/questions/14515200/python-opencv-solvepnp-yields-wrong-translation-vector
          '''
          if pose is None:
              pose = self.pose()
          t, r = pose
          return -np.matrix(cv2.Rodrigues(r)[0]).T * np.matrix(tf camera_position(self, pose=None):
          '''
          returns camera position in world coordinates using self.rvec and self.tvec
          from http://stackoverflow.com/questions/14515200/python-opencv-solvepnp-yields-wrong-translation-vector
          '''
          if pose is None:
              pose = self.pose()
          t, r = pose
          return -np.matrix(cv2.Rodrigues(r)[0]).T * np.matrix(t)
docs: returns camera position in world coordinates using self.rvec and self.tvec
          from http://stackoverflow.com/questions/14515200/python-opencv-solvepnp-yields-wrong-translation-vector