[vtkusers] Structured Pts:Set extents

[Mulhearn James F NPRI]

Can one use the StructuredPoints SetExtents function to clip a portion from a large volume of data for display? I've used ExtractVOI in the past but in reading User' Guide pg 126 appears that one can simply use ImageReader to limit the data for display using the SetDataExtent function. Since my data is in StructuredPoints format would like to use SetExtents function if it does the same thing. 
 Have tried SetExtents but seem to always display the full volume.