performance issues with vtkStructuredGrid and vtkExtractGrid

[Jody Winston]

I am having huge performance decrease of 10 to 20 times when I use
vtkExtractGrid to extract a subset of the VOI from a
vtkStructuredGrid.  The basic program flow to create the grid, find
the extents, extract the extents and then display the data:

    reader = vtkStructuredGridReader()
    reader.SetFileName("Medium.bin")
    reader.Update()

    inputExtents = reader.GetOutput().GetExtent()
    extents = [inputExtents[0], inputExtents[1],
               inputExtents[2], inputExtents[3], 
               0, 64]

    grid = vtkExtractGrid()
    grid.SetInput(sgrid)
    grid.SetVOI(extents[0], extents[1],
                extents[2], extents[3],
                extents[4], extents[5])

The previous fragment runs 10 to 20 times slower than the following
modification:
    extents = [inputExtents[0], inputExtents[1],
               inputExtents[2], inputExtents[3], 
               inputExtents[4], inputExtents[5]]

I have a full program with timing information and data if anyone wants 
to take a look at it.

Jody

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