Python OpenCV：查找曲率切线并检测与另一个圆的交点

Question

I am doing a line detecting software. I can successfully detect the contour of line as array of points. Now I am trying to extract information from it such as approx angle and error from center (see images below).

input image:

output image:

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Output image description:
Yellow circle is area of interest, but centered on intersecting point of red x-axis line and detected line. Center of this circle is marked with big blue point.

Green line is the actual output. After cropped image with yellow circle, I am going to use OpenCV's fitLine function. This will give me my precious point locations, I guess.

What I need:

I want to use, as said above, fitLine method but since I cannot locate the intersecting point -between mid-x-axis and detected white line- I cannot crop image and so on. So, I need to locate the point (shown in big blue point in output image).

Answer 1

I answer my own question on behalf of the power of research:

I realized that circular mask is not needed since I am cropping the image to find average curve, but still managed to crop a circular area just to be sure I can.

After cropping image to work with area of interest, I simply used fitLine method with DIST_L2 distance. That was all I wanted. Note that Python's builtin function sorted was not able to sort my contours by area.