why set direction offset to pi/4?

Hello, is anybody know why set direction offset to pi/4, and subtract it, what dose this mean, as follows:

first subtract self.dir_offset and then add it back again, what's the purpose of this trick, thanks.

dir_rot = limit_period(bboxes[..., 6] - self.dir_offset,
self.dir_limit_offset, np.pi)
bboxes[..., 6] = (
dir_rot + self.dir_offset +
np.pi * dir_scores.to(bboxes.dtype))