已知圆弧上两点坐标及圆半径，计算圆心坐标

已知圆弧上两点坐标及圆半径，计算圆心坐标的JavaScript脚本代码 ，参考http://www.cnblogs.com/lhuan/p/5753847.html  

//
//
//  由圆弧上两点坐标及圆半径，计算圆心坐标的JavaScript脚本代码  
//  参考http://www.cnblogs.com/lhuan/p/5753847.html
//



function Y_Coordinates(  x,  y,  k,  x0)
{
    return k * x0 - k * x + y;
}

function calCircleCenter( p1, p2, r )
{      
    var k = 0.0,k_verticle = 0.0;
    var mid_x = 0.0,mid_y = 0.0;
    var a = 1.0;
    var b = 1.0;
    var c = 1.0;
    var center1 = new Array();
    var center2 = new Array();  


    k = (p2[1] - p1[1]) / (p2[0] - p1[0]);

    if(k == 0)
    {
        center1[0] = (p1[0] + p2[0]) / 2.0;
        center2[0] = (p1[0] + p2[0]) / 2.0;
        center1[1] = p1[1] + Math.sqrt(r * r -(p1[0] - p2[0]) * (p1[0] - p2[0]) / 4.0);
        center2[1] = p2[1] - Math.sqrt(r * r -(p1[0] - p2[0]) * (p1[0] - p2[0]) / 4.0);
    }
    else
    {
        k_verticle = -1.0 / k;
        mid_x = (p1[0] + p2[0]) / 2.0;
        mid_y = (p1[1] + p2[1]) / 2.0;
        a = 1.0 + k_verticle * k_verticle;
        b = -2 * mid_x - k_verticle * k_verticle * (p1[0] + p2[0]);
        c = mid_x * mid_x + k_verticle * k_verticle * (p1[0] + p2[0]) * (p1[0] + p2[0]) / 4.0 - 
            (r * r - ((mid_x - p1[0]) * (mid_x - p1[0]) + (mid_y - p1[1]) * (mid_y - p1[1])));

        center1[0] = (-1.0 * b + Math.sqrt(b * b -4 * a * c)) / (2 * a);
        center2[0] = (-1.0 * b - Math.sqrt(b * b -4 * a * c)) / (2 * a);
        center1[1] = Y_Coordinates(mid_x,mid_y,k_verticle,center1[0]);
        center2[1] = Y_Coordinates(mid_x,mid_y,k_verticle,center2[0]);
    }

    console.log( center1[0] +  "    " + center1[1] );
    console.log( center2[0] + "    " + center2[1] );

}

样例

var point1 = [40, 0] ;

var point2 = [0, 40 ] ;


var radius = 40 


calCircleCenter( point1, point2, radius )

References  

Bezier.js  https://github.com/Pomax/bezierjs
  
A node.js and client-side library for (quadratic and cubic) Bezier curve work.