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 you really want to understand the basics, just go to the basics:

http://www.cs.ubc.ca/~lowe/papers/ijcv04.pdf

It is the first, and one of the most influential papers about image feature description/extraction. You may find it a bit hard to swallow, but it offers a good explanation of a complex problem.