Engine中如何判断要素类是否含有Z值？

String shapeFieldName = featureClass.ShapeFieldName; 

int shapeFieldIndex = featureClass.FindField(shapeFieldName); 

IFields fields = featureClass.Fields; 

IField shapeField = fields.get_Field(shapeFieldIndex); 

IGeometryDef geometryDef = shapeField.GeometryDef;