private Point CorrespondingPoint(Point pt)
{
 double xmin = 0;
 double xmax = 6.5;
 double ymin = -1.1;
 double ymax = 1.1;
 var result = new Point
 {
 X = (pt.X - xmin) * canvas.Width / (xmax - xmin),
 Y = canvas.Height - (pt.Y - ymin) * canvas.Height / (ymax - ymin)
 };
 return result;
}