code: def focal(self):
          
          if self._focal is None:
              # calculate focal length from FOV
              focal = [(px / 2.0) / np.tan(np.radians(fov / 2.0))
                       for px, fov in zip(self._resolution, self.fov)]
              # store as correct dtype
              self._focal = np.asanyarray(focal, dtype=np.float64)
  
          return self._focal
docs: Get the focal length in pixels for the camera.
  
          Returns
          ------------
          focal : (2,) float
            Focal length in pixels