// Get the X position of the pointClicked
                    cx = (double)prePs.X;
                    // Get the Y position of the pointClicked
                    cy = double.Parse(this.plotter.Viewport.Transform.DataTransform.ViewportToData(prePs).Y.ToString());

                    // Get the new X position of the pointClicked by the angel with math calculation
                    xEndP = (float)(double.Parse(txt_enterRadius.Text.ToString()) * Math.Cos(a * Math.PI / 180F)) + cx;
                    // Get the new Y position of the pointClicked by the angel with math calculation
                    yEndP = (float)(double.Parse(txt_enterRadius.Text.ToString()) * Math.Sin(a * Math.PI / 180F)) + cy;

http://sizmedia.com/my.php?i=hm2zuv5yyenj.png