图像轮廓

Mat src = imread("E:/guida.png", -1);
    Mat edge;
    Mat dst = Mat::zeros(src.size(), src.type());
    Canny(src, edge, 3, 9, 3);

一。寻找轮廓并画出轮廓

findcontours函数找出轮廓点的二维集合。

vector<vector<Point>>contours;
    vector<Vec4i>hierarchy;
    findContours(edge, contours, hierarchy, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);
    drawContours(dst, contours, -1, Scalar(255)); 

二。根据轮廓点集得到凸包的点集，并绘制

    //画凸包，需要点集
    vector<vector<Point>>hull(contours.size());
    for (int i = 0; i < contours.size(); i++) {
        convexHull(Mat(contours[i]), hull[i]);
    }
    for (int i = 0; i < contours.size(); i++) {
        drawContours(dst, contours, i, Scalar(255));
        drawContours(dst, hull, i, Scalar(255));
    }

 三。外接矩形 

    Rect rect = boundingRect(contours[0]);
    rectangle(edge, rect, Scalar(255));

 四。最小包围矩形

    //最小包围矩形
    RotatedRect box = minAreaRect(contours[0]);
    Point2f vertex[4];
    box.points(vertex);
    for (int i = 0; i < 4; i++) {
        line(edge, vertex[i], vertex[(i + 1)% 4], Scalar(255));
    }

 五。最小包围圆和三角形

    //最小包围圆
    Point2f center;
    float radius;
    minEnclosingCircle(contours[0], center, radius);
    circle(edge, center, radius, Scalar(255));
　　//最小包围三角形
    vector<Point2f> triangle;
    minEnclosingTriangle(contours[1], triangle);
    for (int i = 0; i < 3; i++)
    line(edge, triangle[i], triangle[(i + 1) % 3], Scalar(255, 255, 0), 1, LINE_AA);

 六。计算点集的逼近多边形，面积，多边形周长

    vector<Point>contour;
    contour.push_back(Point2f(0,0));
    contour.push_back(Point2f(10, 0));
    contour.push_back(Point2f(10, 10));
    contour.push_back(Point2f(5, 4));
    double area0 = contourArea(contour);
    vector<Point>approx;
    approxPolyDP(contour, approx, 5, true);
    
    double area1 = contourArea(approx);
    Mat test = Mat::zeros(Size(50, 50), CV_8UC1);
    Mat test1 = Mat::zeros(Size(50, 50), CV_8UC1);
    for (int i = 0; i < contour.size(); i++)
    {
        line(test, contour[i], contour[(i + 1) % 4], Scalar(255));
    }
    for (int i = 0; i < approx.size(); i++)
    {
        line(test1, approx[i], approx[(i + 1) % approx.size()], Scalar(255));
    }
　　　　double length=arcLength(approx,true);

根据原点集绘制的多边形

 根据逼近多边形绘制的