public override Double Get(Double x, Double y)
{
var dx = x - this.XCenter.Get(x, y);
var dy = y - this.YCenter.Get(x, y);
var len = Math.Sqrt(dx * dx + dy * dy);
var rad = this.Radius.Get(x, y);
var i = (rad - len) / rad;
if (i < 0) i = 0;
if (i > 1) i = 1;
return i;
}