sde栅格数据问题

<P>请问高手，当我用如下代码打开影像数据时，为何<FONT color=#000080>Set</FONT> pSDERasterDataset = pName.Open得不到栅格数据集？
</P><PRE><CODE><FONT color=#000080>Public Function</FONT></CODE> GetRasterFromSDE(sServer <CODE><FONT color=#000080>As String</FONT></CODE>, sInstance <CODE><FONT color=#000080>As String</FONT></CODE>, _
       sDB <CODE><FONT color=#000080>As String</FONT></CODE>, sUser <CODE><FONT color=#000080>As String</FONT></CODE>, sPassword <CODE><FONT color=#000080>As String</FONT></CODE>, sSDERaster <CODE><FONT color=#000080>As String</FONT></CODE>) <CODE><FONT color=#000080>As</FONT></CODE> IRasterDataset
  
   <CODE><FONT color=#008000>' sServer,sInstance,sDB,sUser,sPasswd: ArcSDE connection info</FONT></CODE>
  <CODE><FONT color=#008000>' sSDERaster: the ArcSDE raster dataset name </FONT></CODE>
  
  <CODE><FONT color=#000080>Dim</FONT></CODE> pSDEWs <CODE><FONT color=#000080>As</FONT></CODE> IWorkspaceName
  <CODE><FONT color=#000080>Dim</FONT></CODE> pSDEPropertySet <CODE><FONT color=#000080>As</FONT></CODE> IPropertySet
  <CODE><FONT color=#000080>Dim</FONT></CODE> pSDERasterDataset as IRasterDataset
  <CODE><FONT color=#000080>Dim</FONT></CODE> pDsName <CODE><FONT color=#000080>As</FONT></CODE> IDatasetName
  <CODE><FONT color=#000080>Dim</FONT></CODE> pName <CODE><FONT color=#000080>As</FONT></CODE> IName
  <CODE><FONT color=#000080>Dim</FONT></CODE> sQualifiedName <CODE><FONT color=#000080>As String</FONT></CODE>
  
  
   <CODE><FONT color=#008000>' Get connection propertyset</FONT></CODE>
   <CODE><FONT color=#000080>Set</FONT></CODE> pSDEPropertySet = <CODE><FONT color=#000080>New</FONT></CODE> PropertySet
  <CODE><FONT color=#000080>With</FONT></CODE> pSDEPropertySet
   .SetProperty "Server", sServer
   .SetProperty "Instance", sInstance
   .SetProperty "Database", sDB
   .SetProperty "User", sUser
   .SetProperty "Password", sPassword
   .SetProperty "Version", "SDE.DEFAULT"
  <CODE><FONT color=#000080>End With</FONT></CODE>

   <CODE><FONT color=#008000>' Get workspacename</FONT></CODE>
   <CODE><FONT color=#000080>Set</FONT></CODE> pSDEWs = <CODE><FONT color=#000080>New</FONT></CODE> WorkspaceName
  pSDEWs.ConnectionProperties = pSDEPropertySet
  pSDEWs.WorkspaceFactoryProgID = "esricore.sdeworkspacefactory"

   <CODE><FONT color=#008000>' Get qualified ArcSDE raster name</FONT></CODE>
   if len(sDB) > 0 <CODE><FONT color=#000080>Then</FONT></CODE>
   sQualifiedName = sDB + "." + sUser + "." + sSDERaster
  <CODE><FONT color=#000080>Else</FONT></CODE>
sQualifiedName = sUser + "." + sSDERaster
  <CODE><FONT color=#000080>End If</FONT></CODE>

   <CODE><FONT color=#008000>' Get raster dataset name</FONT></CODE>
   <CODE><FONT color=#000080>Set</FONT></CODE> pDsName = <CODE><FONT color=#000080>New</FONT></CODE> RasterDatasetName
  pDsName.Name = sQualifiedName
  <CODE><FONT color=#000080>Set</FONT></CODE> pDsName.WorkspaceName = pSDEWs
  <CODE><FONT color=#000080>Set</FONT></CODE> pName = pDsName
  
   <CODE><FONT color=#008000>' Open ArcSDE raster dataset</FONT></CODE>
   <CODE><FONT color=#000080>Set</FONT></CODE> pSDERasterDataset = pName.Open
  
   <CODE><FONT color=#008000>' Cleanup</FONT></CODE>
   <CODE><FONT color=#000080>Set</FONT></CODE> GetRasterFromSDE = pSDERasterDataset
  <CODE><FONT color=#000080>Set</FONT></CODE> pSDEWs = <CODE><FONT color=#000080>Nothing
  Set</FONT></CODE> pSDERasterDataset = <CODE><FONT color=#000080>Nothing
  Set</FONT></CODE> pSDEPropertyset = <CODE><FONT color=#000080>Nothing
  Set</FONT></CODE> pName = <CODE><FONT color=#000080>Nothing
  Set</FONT></CODE> pDsName = <CODE><FONT color=#000080>Nothing
  
End Function</FONT></CODE>
</PRE>