private void Update()
{
ILocation center = Center;
if ((ParentMap == null) || (center == null))
{
return;
}
IProjection viewPortProjection = ParentMap.ViewPortProjection;
double scaleFactor = viewPortProjection.CartesianScaleFactor(center);
_ellipse.RadiusY = RadiusY * scaleFactor;
_ellipse.RadiusX = RadiusX * scaleFactor;
_ellipse.Center = viewPortProjection.ToCartesian(center).ToPoint();
InvalidateMeasure();
}