Point3D P1 = ConvertP(new Point(AnT.Width, 0), Z);
Point3D P2 = ConvertP(new Point(AnT.Width, AnT.Height), Z);

public static Point3D ConvertP(Point p, double inZ)
        {
            Point3D P1, P2, Dir;
            double x, y, z;

            int vx = p.X, vy = AnTH - p.Y - 1;
            int[] viewport = new int[4];
            double[] projection = new double[16];
            double[] modelview = new double[16];
            Gl.glGetIntegerv(Gl.GL_VIEWPORT, viewport);
            Gl.glGetDoublev(Gl.GL_PROJECTION_MATRIX, projection);
            Gl.glGetDoublev(Gl.GL_MODELVIEW_MATRIX, modelview);
            int[] zz = new int[1];
            Gl.glReadPixels(vx, vy, 1, 1, Gl.GL_DEPTH_COMPONENT, Gl.GL_FLOAT, zz);
            Glu.gluUnProject(vx, vy, 0, modelview, projection, viewport, out x, out y, out z);
            P1 = new Point3D(x, y, z);
            Glu.gluUnProject(vx, vy, 1, modelview, projection, viewport, out x, out y, out z);
            P2 = new Point3D(x, y, z);
            Dir = new Point3D();
            Dir = P1 - P2;
            Dir.Normalize();

            Point3D A = new Point3D(0, 0, 2 * P1.Z + inZ);
            Point3D n = new Point3D(0, 0, -1);
            double t = n * (A - P1);
            Point3D P = P1 + t * Dir;
            double R = Math.Sqrt(P.X * P.X + P.Y * P.Y + P.Z * P.Z);
            double addz = 0;
            while (Math.Abs(R - inZ) > 0.00001)
            {
                double add= Math.Abs(R - inZ);
                if (R > inZ) addz -= add;
                else addz += add;
                A = new Point3D(0, 0, 2 * P1.Z + inZ + addz);
                n = new Point3D(0, 0, -1);
                t = n * (A - P1);
                P = P1 + t * Dir;
                R = Math.Sqrt(P.X * P.X + P.Y * P.Y + P.Z * P.Z);
            }
            return P;
        }

class Point3D
    {
        public double X, Y, Z;
        public Point3D()
        {
            this.X = 0;
            this.Y = 0;
            this.Z = 0;
        }
        public Point3D(double X, double Y, double Z)
        {
            this.X = X;
            this.Y = Y;
            this.Z = Z;
        }

        public void Normalize()
        {
            double Lenght = Math.Sqrt(X * X + Y * Y + Z * Z);
            this.X /= Lenght;
            this.Y /= Lenght;
            this.Z /= Lenght;
        }

        #region Перегрузка операторов
        public static Point3D operator +(Point3D P1, Point3D P2)
        {
            Point3D tmp = new Point3D();
            tmp.X = P1.X + P2.X;
            tmp.Y = P1.Y + P2.Y;
            tmp.Z = P1.Z + P2.Z;
            return tmp;
        }
        public static Point3D operator -(Point3D P1, Point3D P2)
        {
            Point3D tmp = new Point3D();
            tmp.X = P1.X - P2.X;
            tmp.Y = P1.Y - P2.Y;
            tmp.Z = P1.Z - P2.Z;
            return tmp;
        }
        public static double operator *(Point3D P1, Point3D P2)
        {
            return P1.X * P2.X + P1.Y * P2.Y + P1.Z * P2.Z;
        }
        public static Point3D operator *(double D, Point3D P)
        {

            Point3D tmp = new Point3D();
            tmp.X = P.X * D;
            tmp.Y = P.Y * D;
            tmp.Z = P.Z * D;
            return tmp;
        }
        #endregion
    }