[200 opencv routines] 215 Drawing approximate ellipse based on polyline

OpenCV routine 200 piece General catalogue

【youcans Of OpenCV routine 200 piece 】215. Draw approximate ellipses based on polylines

If you need more control over ellipse rendering , Or draw a rough elliptical boundary , have access to cv.ellipse2Poly Retrieve curve , Then render with polylines or use fillPoly Fill in .

The function prototype ：

cv.ellipse2Poly(center, axes, angle, arcStart, arcEnd, delta[,]) → pts

Parameter description ：

• img： Input / output image , Allows single channel grayscale images or multi-channel color images
• center： Coordinates of the center point of the ellipse ,(x, y) Tuple of format
• axes： Length of ellipse semi axis ,(hfirst, hsecond) Tuple of format -
• angle： Ellipse edge x Rotation angle in the axis direction （ Angle system , clockwise ）
• arcStart： The starting angle of the elliptical arc （ Angle system ）
• endAngle： The ending angle of an elliptical arc （ Angle system ）
• delta： The angle with the next line segment , Used to control approximate accuracy , The smaller the angle, the closer it is to the ellipse
• pts： Output vector , An array of vertex coordinates of a polyline approximating an elliptical arc

    # A4.6  Draw approximate ellipses based on polylines 
    img = np.ones((400, 600, 3), np.uint8)*224

    cx, cy = 100, 150
    halfAxesLength = (70, 40)
    angle, startAng, endAng = 30, 0, 360
    delta = [10, 20, 30, 40]
    for i in range(len(delta)):
        color = (i*60, i*60, 255-i*60)
        pts = cv.ellipse2Poly((cx+140*i, cy), halfAxesLength, angle, startAng, endAng, delta[i])  # (351,2)
        points = np.array(pts)
        cv.polylines(img, [points], True, color, thickness=1)  #  Draw approximate polygons 
        points[:,1] += 160
        cv.fillPoly(img, [points], color)  #  Draw fill approximation polygons 
        text1 = "delta={}".format(delta[i])
        text2 = "num={}".format(pts.shape)
        cv.putText(img, text1, (140*i+25, 30), cv.FONT_HERSHEY_SIMPLEX, 0.5, 255)
        cv.putText(img, text2, (140*i+25, 50), cv.FONT_HERSHEY_SIMPLEX, 0.5, 255)
        print(pts.shape, points.shape)

    plt.figure(figsize=(9, 6))
    plt.title("Polygon approximated ellipse"), plt.axis('off')
    plt.imshow(cv.cvtColor(img, cv.COLOR_BGR2RGB))
    plt.show()

---

【 At the end of this section 】

Copyright notice ：
[email protected] Original works , Reprint must be marked with the original link ：(https://blog.csdn.net/youcans/article/details/125468099)
Copyright 2022 youcans, XUPT
Crated：2022-6-26
Welcome to your attention 『youcans Of OpenCV routine 200 piece 』 series , Ongoing update
Welcome to your attention 『youcans Of OpenCV Learning lessons 』 series , Ongoing update

210. There are so many holes in drawing a straight line ？
211. Draw vertical rectangle
212. Draw a slanted rectangle
213. Draw a circle
214. Detailed explanation of parameters for drawing ellipse
215. Draw approximate ellipses based on polylines