点到直线的距离

      /// /****点到直线的距离***
        /* 过点（x1,y1）和点（x2,y2）的直线方程为：KX -Y + (x2y1 - x1y2)/(x2-x1) = 0
        * 设直线斜率为K = (y2-y1)/(x2-x1),C=(x2y1 - x1y2)/(x2-x1)
        * 点P(x0,y0)到直线AX + BY +C =0DE 距离为：d=|Ax0 + By0 + C|/sqrt(A*A + B*B)
        * 点（x3,y3）到经过点（x1,y1）和点（x2,y2）的直线的最短距离为：
        * distance = |K*x3 - y3 + C|/sqrt(K*K + 1)
        */

        public double CalOffDistance(GCD gcd, Point3d polylineStartPoint, Point3d polylineEndPoint)
        {
            double k = (polylineStartPoint.X - polylineEndPoint.X) / (polylineStartPoint.Y - polylineEndPoint.Y);
            double c = (polylineStartPoint.Y * polylineEndPoint.X - polylineEndPoint.Y * polylineStartPoint.X) / (polylineStartPoint.Y - polylineEndPoint.Y);
            if (polylineStartPoint.Y == polylineEndPoint.Y)
            {
                return Math.Abs(gcd.GcdY - polylineEndPoint.Y);
            }
            return Math.Abs(k * gcd.GcdY - gcd.GcdX + c) / Math.Sqrt(k * k + 1);
        }