void PlotPanelPaint(object sender, PaintEventArgs e)
{
Graphics g = e.Graphics;
var borderPen = new Pen (Brushes.Black,1);
g.DrawRectangle (borderPen, (float)panel1.Bounds.X, (float)panel1.Bounds.Y, (float)panel1.Bounds.Width, (float)panel1.Bounds.Height);
borderPen.Dispose ();
float a = panel1.Height / 4;
var dc = new DrawCylinder (this, a, 2 * a);
dc.DrawIsometricView (g);
}