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Editorial Team
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Asked: 2026-06-14T17:48:00+00:00

I have a problem understanding how OpenCV works when it comes to RotatedRect. I

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I have a problem understanding how OpenCV works when it comes to RotatedRect.

I have extracted a contour and I then try to fit a rotated rectangle over it. The angles that I keep getting range only in 0 to -90. Even if I have the contour directing the other way by flipping it, I still get 0 to -90 angles.

My problem is to make sure the contour lies at 0′ degrees. And for that I have to calculated the orientation and then rotate accordingly.

How are these angles represented in OpenCV (2.4.3)?

Regards
Wajih

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1 Answer

  1. Editorial Team

    In some cases RotatedRect angle can be the same for contour rotated 180 deg. The best way to figure out if it happens in your case is to draw fitted RotatedRect.

    I think that more suited for your case are contour moments.

    See my answers there:
    Rotation and scale invariant template matching in OpenCV
    and there:
    Find the orientation of an image

    You can compute moments with cv::Moments : http://docs.opencv.org/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html?highlight=moments#cv.Moments

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