OpenCV KeyPoint: information about angle and octave

Question

I want to know more about KeyPoints, so can anyone told me what are

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KeyPoint::angle

In OpenCV docs was mentioned that angle is computed orientation of the

Answer 1

If someone came to this question wondering why does keypoint.octave have such a weird value (e.g. 16253184), it is because it actually carries the information on:

• the actual octave in the least significant byte of the keypoint.octave field
• the layer of that octave in the second least significant byte of the keypoint.octave field
• something else that gets packed into the third least significant byte by the SIFT keypoint detection, but doesn't get used by the SIFT descriptor

keypoint.octave gets unpacked into the variables octave, layer, and scale (scale is just 1/2^octave) with the method unpackOctave (see OpenCV implementation).

To get a visual understanding of variables octave and layer, this image might help: