CODEWITHSUNDEEP
pythonopencv
peter
peter

Reputation: 31

Opencv ellipse() bug?

cv.ellipse( img, center, axes, angle, startAngle, endAngle, color[, thickness[, lineType[, shift]]] )

The startAngle is the starting angle of the elliptic arc in degrees.If we set angele=30 and startAngle=60,the angle of the starting line of the ellipse may be 30+60=90.Is that right? But this is not the case. My code:

img2 = np.zeros((500, 500))
img2 = cv2.ellipse(img2, (250, 250), (120, 40), 30, 60, 180, 255, -1)
cv2.imshow('2', img2)
cv2.waitKey(0)

Lets look at the result, the angle of the starting line(red line) is obviously not 90 degrees.

enter image description here

Why?Is it a bug?

Upvotes: 1

Views: 306

Answers (1)

peter
peter

Reputation: 31

I got it. startAngle is not the starting angle based on the ellpise.It is based on the circumcircle of that ellipse.Lets look at the following figure

enter image description here

It does a mapping operation.The blue curve is the output.

Upvotes: 2

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