template<typename _tp>struct Circle_{    _tp x;    _tp y;    _tp r;};typedef Circle_<float> Circle3f;// This function is based on Modified Least Square Methods from Paper// "A Few Methods for Fitting Circles to Data".void FitCircle(const std::vector<cv::Point2f> &vecPoints, Circle3f &circle){    double Sx = 0., Sy = 0., Sxx = 0., Sx2 = 0., Sy2 = 0., Sxy = 0., Syy = 0., Sx3 = 0., Sy3 = 0., Sxy2 = 0., Syx2 = 0.;    for ( const auto &point : vecPoints )   {        Sx   += point.x;        Sy   += point.y;        Sx2  += point.x * point.x;        Sy2  += point.y * point.y;        Sxy  += point.x * point.y;        Sx3  += point.x * point.x * point.x;        Sy3  += point.y * point.y * point.y;        Sxy2 += point.x * point.y * point.y;        Syx2 += point.y * point.x * point.x;    }    double A, B, C, D, E;    int n = vecPoints.size();    A = n * Sx2 - Sx * Sx;    B = n * Sxy - Sx * Sy;    C = n * Sy2 - Sy * Sy;    D = 0.5 * ( n * Sxy2 - Sx * Sy2 + n * Sx3 - Sx * Sx2 );    E = 0.5 * ( n * Syx2 - Sy * Sx2 + n * Sy3 - Sy * Sy2 );    auto AC_B2 = ( A * C - B * B);  // The variable name is from AC - B^2    auto am = ( D * C - B * E ) / AC_B2;    auto bm = ( A * E - B * D ) / AC_B2;    double rSqureSum = 0.f;    for ( const auto &point : vecPoints )    {        rSqureSum += sqrt ( ( point.x - am ) * ( point.x - am ) + ( point.y - bm) * ( point.y - bm) );    }    auto r = rSqureSum / n;    circle.x = static_cast<float>( am );    circle.y = static_cast<float>( bm );    circle.r = static_cast<float>( r );}void TestFitCircle(){    std::vector<cv::Point2f> vecPoints;    vecPoints.push_back(cv::Point2f(0, 10));    vecPoints.push_back(cv::Point2f(0.1f, 10.1f));    vecPoints.push_back(cv::Point2f(10, 0));    vecPoints.push_back(cv::Point2f(10, 20));    vecPoints.push_back(cv::Point2f(20, 10));    Circle3f circle;     FitCircle(vecPoints, circle);    cout << "X, Y " <<circle.x << ", " << circle.y << "    r " << circle.r << endl;}