Keypoint orientation with the oFAST from Rublee's ORB

1. How does Orb feature detector work?
2. What are orb features?
3. How does Orb work in Opencv?
4. Is orb rotation invariant?

How does Orb feature detector work?

ORB uses BRIEF descriptors but as the BRIEF performs poorly with rotation. So what ORB does is to rotate the BRIEF according to the orientation of keypoints. Using the orientation of the patch, its rotation matrix is found and rotates the BRIEF to get the rotated version.

What are orb features?

ORB has the following key qualities compared to other feature types: Efficient; Outstanding performance-quality tradeoff. Resistant to image noise. Rotation invariant. Multi-scale.

How does Orb work in Opencv?

ORB is basically a fusion of FAST keypoint detector and BRIEF descriptor with many modifications to enhance the performance. First it use FAST to find keypoints, then apply Harris corner measure to find top N points among them. It also use pyramid to produce multiscale-features.

Is orb rotation invariant?

ORB, a very fast binary descriptor based on BRIEF, which is rotation invariant and resistant to noise.