得到指定图层的高程基准（c++） ArcObject

dan::DString ArcmapLayer::getVertialSystem()
{
  IGeoDatasetPtr ipGeoDataset = getFeatureClass();
  BSTR verticalSystemName;
  ISpatialReferencePtr  ipSpatialRefrence;
  ipGeoDataset->get_SpatialReference(&ipSpatialRefrence);
  ISpatialReference3Ptr iSpatialRefer = ipSpatialRefrence;
  IVerticalCoordinateSystemPtr ipVerticalCoordinate;
  iSpatialRefer->get_VerticalCoordinateSystem(&ipVerticalCoordinate);
  ipVerticalCoordinate->get_Name(&verticalSystemName);
  dan::DString aDString = dan::DString::fromWCharArray((LPCTSTR)_bstr_t(verticalSystemName, false));
  ::SysFreeString(verticalSystemName);
  return aDString;
}