指定圆心、半径，创建一个圆。IGraphicsContainer

///
        /// 指定圆心半径，创建一个圆。IGraphicsContainer
        ///
        /// 圆心
        /// 半径
        public void DrawCircle_Graphics(IPoint pPoint, double radius)
        {

            #region 定义填充颜色与类型
            IRgbColor pColor = new RgbColorClass();//颜色
            pColor.RGB = System.Drawing.Color.FromArgb(0, 0, 255).ToArgb();//(B,G,R)

            ILineSymbol pLineSymbol = new SimpleLineSymbolClass();//产生一个线符号对象
            pLineSymbol.Width = 2;
            pLineSymbol.Color = pColor;

            IFillSymbol pFillSymbol = new SimpleFillSymbolClass();//设置填充符号的属性
            pColor.Transparency = 0;
            pFillSymbol.Color = pColor;
            pFillSymbol.Outline = pLineSymbol;
            #endregion

            IConstructCircularArc pConstructCircularArc = new CircularArcClass();
            pConstructCircularArc.ConstructCircle(pPoint, radius, false);
            ICircularArc pArc = pConstructCircularArc as ICircularArc;
            ISegment pSegment1 = pArc as ISegment; //通过ISegmentCollection构建Ring对象
            ISegmentCollection pSegCollection = new RingClass();
            object o = Type.Missing; //添加Segement对象即圆
            pSegCollection.AddSegment(pSegment1, ref o, ref o); //QI到IRing接口封闭Ring对象，使其有效

            IRing pRing = pSegCollection as IRing;
            pRing.Close(); //通过Ring对象使用IGeometryCollection构建Polygon对象
           
            IGeometryCollection pGeometryColl = new PolygonClass();
            pGeometryColl.AddGeometry(pRing, ref o, ref o); //构建一个CircleElement对象

            IElement pElement = new CircleElementClass();
            pElement.Geometry = pGeometryColl as IGeometry;

            //填充圆的颜色
            IFillShapeElement pFillShapeElement = pElement as IFillShapeElement;
            pFillShapeElement.Symbol = pFillSymbol;

            IGraphicsContainer pGC = this.axMapControl1.ActiveView.GraphicsContainer;
            pGC.AddElement(pElement, 0);
            this.axMapControl1.Refresh();
        }