The matching performance of BRIEF falls off sharply for in-plane rotation of more than a few degrees. ORB proposes a method to steer BRIEF according to the orientation of the keypoints. For any feature set of n binary tests at location (xi, yi), we need the 2 x n matrix:
We use the patch orientation θ and the corresponding rotation matrix Rθ, and construct a steered version Sθ of S:
Now, the steered BRIEF operator becomes:
We discretize ...