///////////////////////////////////////////
//求三角形外接圆圆心坐标
///////////////////////////////////////////
void circle_center(Point *center,Point pt[3],double *radiu)
{
double x1,x2,x3,y1,y2,y3;
double x = 0;
double y = 0;
x1 = pt[0].pt.x;
x2 = pt[1].pt.x;
x3 = pt[2].pt.x;
y1 = pt[0].pt.y;
y2 = pt[1].pt.y;
y3 = pt[2].pt.y;
x=((y2-y1)*(y3*y3-y1*y1+x3*x3-x1*x1)-(y3-y1)*(y2*y2-y1*y1+x2*x2-x1*x1))/(2*(x3-x1)*(y2-y1)-2*((x2-x1)*(y3-y1)));
y=((x2-x1)*(x3*x3-x1*x1+y3*y3-y1*y1)-(x3-x1)*(x2*x2-x1*x1+y2*y2-y1*y1))/(2*(y3-y1)*(x2-x1)-2*((y2-y1)*(x3-x1)));
center->pt.x = x ;
center->pt.y = y ;
*radiu = (pt[0].pt.x - x)*(pt[0].pt.x - x) + (pt[0].pt.y - y)*(pt[0].pt.y - y);
}