code: def direction(self):
          
          direction = np.dot(self.primitive.transform[:3, :3],
                             [0.0, 0.0, np.sign(self.primitive.height)])
          return direction
docs: Based on the extrudes transform, what is the vector along
          which the polygon will be extruded
  
          Returns
          ---------
          direction: (3,) float vector. If self.primitive.transform is an
                     identity matrix this will be [0.0, 0.0, 1.0]