Question

基本上，我有一个包含对象的二进制图像，我应用了轮廓和矩函数来查找质心，并检测此图像中的对象。（不规则物体）

我现在要做的是生成穿过质心，到轮廓边缘的线（以不同的角度），找出最长的线。

有关此事的任何帮助将不胜感激。

Answer 1

假设线条从质心绘制到质量的周边，而不是使用测试角度，只需使用轮廓点本身并对每组点进行距离计算。见下面的例子。（示例代码是用C ++编写的，问题标签是java，有一天我会被烧掉。）

    Mat GrayImage; // input grayscale image, set to something
    Mat ContourImage;
    Mat DrawImage = Mat::zeros(GrayImage.size(), CV_8UC3);
    int thresh = 90;
    // get a threshold image using Canny edge detector
    Canny(GrayImage, ContourImage, thresh, thresh * 2, 3);
    vector< vector<Point> > contours;
    vector<Vec4i> hierarchy;
    findContours(ContourImage, contours, hierarchy, CV_RETR_EXTERNAL, CV_CHAIN_APPROX_SIMPLE);// retrieves external contours, CHANGES THRESHOLD IMAGE   

    vector<Point2f> centerofMass(contours.size());
    vector<Moments> mu(contours.size());
    // for every contour in the image
    for (int i = 0; i < contours.size(); i++)
    {
        // draw the contour
        drawContours(DrawImage, contours, i, Scalar(200, 54, 120), 2, 8, hierarchy, 0, Point());
        //calculate center of mass
        mu[i] = moments(contours[i],false);
        centerofMass[i] = Point2f(mu[i].m10 / mu[i].m00, mu[i].m01 / mu[i].m00);

        double biggestDistance = 0;
        Point2f farthest_Perimeter_Point;
        // for each point in the current contour
        for (int j = 0; j < contours[i].size(); j++)
        {
            // get a point that makes up the contour
            Point2f perimeterofMass(contours[i][j].x, contours[i][j].y);
            //calculate the distance
            double dist = cv::norm(centerofMass[i] - perimeterofMass);
            // determine farthest point
            if (dist > biggestDistance)
            {
                biggestDistance = dist;
                farthest_Perimeter_Point = perimeterofMass;
            }
        }
        // now we have farthest point as farthest_Perimeter_Point for the current contour at [i]
        //draw the line because why not;
        line(DrawImage, centerofMass[i], farthest_Perimeter_Point, Scalar(145, 123, 201));
    }
    imshow("grayimage", GrayImage);
    imshow("thresholdimage", ContourImage);
    imshow("drawimage", DrawImage);

另一个假设是线条从质量周边的一个起点到质量的另一侧绘制，同时与中心相交。首先从周长的一个点开始，使用起点和中心点在point-intercept form中形成线方程。第二个找到此线与另一侧相交的位置，现在您可以计算距离。第三，确定这些线之间的最大距离。

参考文献：

Opencv 2.4.11 Java：从质心到轮廓边缘绘制线条

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