请教AE 中3D高人指点几个问题!!

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<P ><FONT face="Times New Roman">1.<FONT size=3>       </FONT></FONT>怎样在<FONT face="Times New Roman">Arcgis Engine </FONT>中如何实现调整<FONT face="Times New Roman">featurelayer</FONT>的基准高度<FONT face="Times New Roman">?</FONT>如上图所示</P>
<P ><FONT face="Times New Roman">2.<FONT size=3>       </FONT></FONT>在<FONT face="Times New Roman">Arcgis Engine </FONT>中有设置<FONT face="Times New Roman">FeatureLayer</FONT>拉伸的函数</P><PRE><FONT face=宋体>Public Sub SetLayerExtrusionString(sLayer, sExtrusionExpression As String)</FONT></PRE><PRE><FONT face=宋体>   On Error GoTo err</FONT></PRE><PRE><FONT face=宋体>    If Not TypeOf Application Is ISxApplication Then Exit Sub</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>'   in ArcScene VBA...</FONT></PRE><PRE><FONT face=宋体>'   get the document</FONT></PRE><PRE><FONT face=宋体>    Dim pSxDoc As ISxDocument</FONT></PRE><PRE><FONT face=宋体>    Set pSxDoc = Application.Document</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>'   get the Scene from the Document:</FONT></PRE><PRE><FONT face=宋体>    Dim pScene As IScene</FONT></PRE><PRE><FONT face=宋体>    Set pScene = pSxDoc.Scene</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>'   get the layer in the scene:</FONT></PRE><PRE><FONT face=宋体>    Dim pLayer As ILayer</FONT></PRE><PRE><FONT face=宋体>    Set pLayer = GetLayer(sLayer)   </FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>'   get layer extensions:</FONT></PRE><PRE><FONT face=宋体>    Dim pLayerExts As ILayerExtensions</FONT></PRE><PRE><FONT face=宋体>    Set pLayerExts = pLayer</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>'   get the 3D properties from extension:</FONT></PRE><PRE><FONT face=宋体>'   layer must have it if it is in scene:</FONT></PRE><PRE><FONT face=宋体>    Dim i As Long</FONT></PRE><PRE><FONT face=宋体>    For i = 0 To pLayerExts.ExtensionCount - 1</FONT></PRE><PRE><FONT face=宋体>        Dim p3DProps As I3DProperties</FONT></PRE><PRE><FONT face=宋体>        Set p3DProps = pLayerExts.Extension(i)</FONT></PRE><PRE><FONT face=宋体>        If (Not p3DProps Is Nothing) Then</FONT></PRE><PRE><FONT face=宋体>            Exit For</FONT></PRE><PRE><FONT face=宋体>        End If</FONT></PRE><PRE><FONT face=宋体>    Next</FONT></PRE><PRE><FONT face=宋体>    p3DProps.ExtrusionExpressionString = sExtrusionExpression</FONT></PRE><PRE><FONT face=宋体>    p3DProps.ExtrusionType = esriExtrusionMinZ</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>'   Tell the scene graph to invalidate the layer and redraw:</FONT></PRE><PRE><FONT face=宋体>    Dim pSG As ISceneGraph</FONT></PRE><PRE><FONT face=宋体>    Set pSG = pScene.SceneGraph</FONT></PRE><PRE><FONT face=宋体>    pSG.Invalidate pLayer, True, True</FONT></PRE><PRE><FONT face=宋体>    pSG.RefreshViewers</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>    Exit Sub</FONT></PRE><PRE><FONT face=宋体>    </FONT></PRE><PRE><FONT face=宋体>err:</FONT></PRE><PRE><FONT face=宋体>End Sub</FONT></PRE>
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<P >我想问下怎样实现一个把一个<FONT face="Times New Roman">featurelayer</FONT>中某个字段如要拉伸的值关联起来<FONT face="Times New Roman">!? </FONT>即<FONT face="Times New Roman">sExtrusionExpression </FONT>这个变量是不是就是<FONT face="Times New Roman">featurelayer</FONT>的字段值<FONT face="Times New Roman">!!</FONT></P>
<P ><FONT face="Times New Roman">3.<FONT size=3>       </FONT></FONT>为什么一个<FONT face="Times New Roman">layer</FONT>有多个<FONT face="Times New Roman">extension?</FONT></P>
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<P>你可以去arcscripts.esri.com看一个arcmap 3d viewer的例子，他演示了如何改变基准高度</P><P>关联的例子在帮助里有了，你可以look look</P>