System information (version)

• OpenCV => 4.2
• Operating System / Platform => Ubuntu 18.04
• Compiler => Python 3.8

Detailed description

minAreaRect is supposed to provide an angle as part of a rotated bounding box of a contour. It works fine in most cases, but I encountered multiple cases where a wrong angle is returned. I first saw this issue when using the python implementation, but can confirm this is also happening in C++.

Steps to reproduce

Python code:

     contour = np.loadtxt("defect_contour.txt").reshape(-1, 1, 2).astype(np.int32)
    rect = cv.minAreaRect(contour)  # xy, wh, angle
    box = cv.boxPoints(rect) # cv2.boxPoints(rect) for OpenCV 3.x
    box = np.int0(box)    
    cv.imwrite("defect_contour.png", cv.drawContours(np.zeros((2208, 3216)),[box, contour],-1,255,5))

Using this contour:
defect_contour.txt

The resulting image will look like this:

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc