Silverlight中在BingMap上画一个圆

不解释，直接上代码：

private double rad(double d)
{
	return d * Math.PI / 180;
}
//radius : km
private void DrawCircle(Location center, double radius)
{
	double EARTH_RADIUS = 6371;

	double lon = rad(center.Longitude);
	double lat = rad(center.Latitude);

	double d = radius / EARTH_RADIUS;
	polygon = new MapPolygon()
	{
		Fill = new SolidColorBrush(Colors.Red),
		Opacity = 0.6,
	};
	polygon.Locations = new LocationCollection();

	for (int i = 0; i < 360; i++)
	{
		Location location = new Location();
		double bearing = rad(i);
		location.Latitude = Math.Asin(Math.Sin(lat) * Math.Cos(d) + Math.Cos(lat) * Math.Sin(d) * Math.Cos(bearing));
		location.Longitude = ((lon + Math.Atan2(Math.Sin(bearing) * Math.Sin(d) * Math.Cos(lat), Math.Cos(d) - Math.Sin(lat) * Math.Sin(location.Latitude))) * 180) / Math.PI;
		location.Latitude = location.Latitude * 180 / Math.PI;
		polygon.Locations.Add(location);
	}
	MyMap.Children.Insert(0, polygon);
}