请教一个engine中实现捕捉功能的问题

<P>各位，请教一个engine中实现捕捉功能的问题。</P>
<P>我现在通过hittest已经得到了捕捉点，我想像arcmap的sketch工具一样，通过一个小圆圈表示当前捕捉到的点。</P>
<P>请问通过什么方法绘制这个小圆圈比较好？ 多谢！</P>
<P>我现在是通过element来绘制的，但对鼠标轨迹的擦除不是很好，总是有些痕迹的残留。代码如下：</P>
<P>捕捉鼠标绘制<BR>Dim pCurrentSymbol As ISimpleMarkerSymbol<BR>pCurrentSymbol = New SimpleMarkerSymbol<BR>With pCurrentSymbol<BR>     .Outline = True<BR>     .OutlineSize = 0.2<BR>     .OutlineColor = GetRGBColor(0, 0, 0)<BR>     .Color = GetRGBColor(0, 200, 240, 0)<BR>     .Style = esriSimpleMarkerStyle.esriSMSSquare<BR>     .Size = 6<BR>End With</P>
<P>Dim pPointGeo As IGeometry<BR>pPointGeo = m_pPoint     'm_pPoint是捕捉到的点，从窗体传入类中的<BR>Dim pElement As IElement<BR>Dim pME As IMarkerElement<BR>pME = New MarkerElement<BR>pElement = pME<BR>pElement.Geometry = pPointGeo<BR>pME.Symbol = pCurrentSymbol</P>
<P>Dim pGraphicsContainer As IGraphicsContainer<BR>pGraphicsContainer = GetMap()<BR>pGraphicsContainer.DeleteAllElements()<BR>pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, pElement, Nothing)<BR>pGraphicsContainer.AddElement(pElement, 0)</P>
<P>Dim pEnve As IEnvelope               ’用于擦除鼠标轨迹的矩形区域<BR>If m_pOldPoint Is Nothing Then      <BR>         m_pOldPoint.PutCoords(m_pPoint.X, m_pPoint.Y)<BR>End If<BR>pEnve = m_pOldPoint.Envelope<BR>pEnve.Height = 10<BR>pEnve.Width = 10<BR>pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, Nothing, pEnve)</P>
<P>pActiveView.PartialRefresh(esriViewDrawPhase.esriViewGraphics, pElement, Nothing)</P>
<P>m_pOldPoint = m_pPoint</P>

Public Sub SnapAfterDraw(iViewDrawPhase As Long)<BR>On Error GoTo SnapAfterDraw_Err<BR>   Dim pScreenDisplay As IScreenDisplay<BR>   Dim iHDC As Long<BR>   <BR>   If iViewDrawPhase = esriViewForeground Then<BR>   <BR>      If Not m_SnapGeometry Is Nothing Then<BR>           <BR>           Set pScreenDisplay = m_pActvieView.ScreenDisplay<BR>           iHDC = pScreenDisplay.hDC<BR>           <BR>           If m_SnapSymbol Is Nothing Then SetSnapSymbol<BR>           <BR>           pScreenDisplay.StartDrawing iHDC, -1<BR>           pScreenDisplay.SetSymbol m_SnapSymbol<BR>           pScreenDisplay.DrawPoint m_SnapGeometry<BR>           pScreenDisplay.FinishDrawing<BR>           <BR>           Set m_SnapGeometry = Nothing<BR>           <BR>      End If<BR>      <BR>   End If<BR>   <BR>    Exit Sub<BR>SnapAfterDraw_Err:<BR>  MsgBox Err.Description, vbInformation, "系统消息"<BR>End Sub