ArcGIS API for Silverlight 在地图上画圆

        //Silverlight前台添加 Graphicslayer 图层
        <esri:Graphicslayer ID="MyGraphicslayer"  Opacity="0.5"/> 
        /// <summary>
        /// ArcGIS API for Silverlight 画圆
        /// </summary>
        /// <param name="radius">圆的半径</param>
        /// <param name="centerP">圆心的点</param>
        /// <param name="graphicslayer">Graphicslayer图层</param>
        public void GetEllipseGraphic(double radius,MapPoint centerP,Graphicslayer graphicslayer)
        {
            Graphic result = new Graphic();
            List<MapPoint> points = new List<MapPoint>();
            for (double i = 0; i <= 360; i++)
            {
                points.Add(new MapPoint((centerP.X - Math.Cos(Math.PI * i / 180.0) * radius),(centerP.Y - Math.Sin(Math.PI * i / 180.0) * radius)));
            }
            ESRI.ArcGIS.Client.Geometry.PointCollection pCollection = new ESRI.ArcGIS.Client.Geometry.PointCollection(points);
            ESRI.ArcGIS.Client.Geometry.polygon g = new ESRI.ArcGIS.Client.Geometry.polygon();
            g.Rings.Add(pCollection);
            result.Geometry = g;
            SimpleFillSymbol sfs = new SimpleFillSymbol();
            sfs.BorderBrush = new SolidColorBrush(Colors.Red);
            sfs.BorderThickness = 2;
            sfs.Fill = new SolidColorBrush(Colors.DarkGray);
            result.Symbol = sfs;
            graphicslayer.Graphics.Add(result);
        }