code: def _axis_in_detector(geometry):
      
      du, dv = geometry.det_axes_init
      axis = geometry.axis
      c = np.array([np.vdot(axis, du), np.vdot(axis, dv)])
      cnorm = np.linalg.norm(c)
  
      # Check for numerical errors
      assert cnorm != 0
  
      return c / cnorm
docs: A vector in the detector plane that points along the rotation axis.