c++ 圆上任意点坐标计算_三点确定一个圆的算法（C++代码）

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QPointF tcircle(QPointF pt1, QPointF pt2, QPointF pt3, double &radius)

{

double x1 = pt1.x(), x2 = pt2.x(), x3 = pt3.x();

double y1 = pt1.y(), y2 = pt2.y(), y3 = pt3.y();

double a = x1 - x2;

double b = y1 - y2;

double c = x1 - x3;

double d = y1 - y3;

double e = ((x1 * x1 - x2 * x2) + (y1 * y1 - y2 * y2)) / 2.0;

double f = ((x1 * x1 - x3 * x3) + (y1 * y1 - y3 * y3)) / 2.0;

double det = b * c - a * d;

if( fabs(det)

{

radius = -1;

return QPointF(0,0);

}

double x0 = -(d * e - b * f) / det;

double y0 = -(a * f - c * e) / det;

radius = hypot(x1 - x0, y1 - y0);

return QPointF(x0, y0);

}