OpenCV:如何在图像上绘制圆形轮廓 [英] Opencv: How to draw a circle contour on an image

问题描述

我已经编写了一个python函数，该函数应该在图像上绘制一个圆，该圆的中心点已使用鼠标回调来定义:

I have written a python function, which is supposed to draw a circle on an image, where the center point of the circle has been defined using a mouse call back:

def draw_circle_contour(frame, pt, radius):
    cv2.circle(frame, center=pt, radius=3, color=(255,0,0), thickness=-1)
    discretized_circle_contour_x = [pt[0] + radius*np.cos(theta) for theta in np.linspace(0, 36, 36)]
    discretized_circle_contour_x = map(int, discretized_circle_contour_x)
    discretized_circle_contour_y = [pt[1] + radius*np.sin(theta) for theta in np.linspace(0, 36, 36)]
    discretized_circle_contour_y = map(int, discretized_circle_contour_y)
    discretized_circle_contour = zip(discretized_circle_contour_x, discretized_circle_contour_y)
    for el in discretized_circle_contour:
        cv2.circle(frame, center=el, radius=2, color=(255,0,0), thickness=-1)

现在，当我将theta指定在np.linspace(0,360,360)之内时，这将非常有效.但是，我现在只想绘制一个圆的1/10. IE.我想绘制一个圆形轮廓，其中被遮盖的角度为36°.我认为这段代码应该可以工作，但是由于某种原因，运行它时，结果看起来像这样:

Now, this works perfectly when I specify theta to be within np.linspace(0,360,360). However, I only want to draw 1/10 of a circle now. I.e. I want to draw a circle contour where the angle that is being covered is 36°. I figured this code should work, but for some reason when I run it, the result looks like this:

这是怎么回事?谁能告诉?

What is going on here? Can anyone tell?

正如您所指出的:除了绘制小圆圈/点外，我还可以使用cv2.polylines绘制圆弧段.只需将最后两行替换为:

As you have pointed out: Instead of drawing little circles/points I could also use cv2.polylines to draw a circle segment. This simply requires the last two lines to be replaced with:

for el in discretized_circle_contour:
        help.append(list(el))
    cv2.polylines(frame, [np.asarray(help)], isClosed=False, color=(255,0,0), thickness=1) 

但是，我仍然面临着这个线段被绘制多次的问题，而我希望在[0,36]度之间仅绘制一次！

However, I am still facing the issue that this segment gets drawn multiple times, while I want it to be drawn only once in between [0,36] degrees!

...，我只是发现了原因:角度theta需要以弧度而不是度为单位.哎呀

... and I just found the reason for that: the angle theta needs to be given in radians, not in degrees. Whops.

最终结果如下:

推荐答案

正在发生的事情是，您在discretized_circle_contour.

What's happening is, you're drawing a filled circle with radius 2 (which looks like a dot, because the radius is very small) in each point in discretized_circle_contour.

如果我正确理解了您的问题，那么您真正想要的只是一个跨过半径1/10的弧形. 您已经有了[0，36]度的拱门点，只需将其绘制为多段线即可:

If I understand your question correctly, what you actually want is just an arch spanning 1/10th of the radius. You already have the points for the arch in [0, 36] degrees, just draw it as a polyline instead:

cv2.polylines(frame, [discretized_circle_contour], False, 1)

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