code: def tilt(poly):
      
      num = len(poly) - 1
      vec = unit_normal(poly[0], poly[1], poly[num])
      vec_alt = np.array([vec[0], vec[1], vec[2]])
      vec_z = np.array([0, 0, 1])
      # return (90 - angle2vecs(vec_alt, vec_z)) # update by Santosh
      return angle2vecs(vec_alt, vec_z)
docs: Tilt of a polygon poly