title: OpenCV KeyPoint: information about angle and octave
body: <p>I want to know more about KeyPoints, so can anyone told me what are</p>
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  <h3>KeyPoint::angle</h3>
  <p>In OpenCV docs was mentioned that angle is computed orientation of the keypoint (-1 if not applicable). I can not imagine that what it is about. So Can anyone say me what it means or bring a small example.</p>
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  <h3>KeyPoint::octave</h3>
  <p>In OpenCV docs was mentioned that octave is octave (pyramid layer) from which the keypoint has been extracted. I can not imagine that what it is about. So Can anyone say me what it means or bring a small example.</p>