[vtkusers] vtkExtractUnstructuredGrid produces no output

[Andrew Porter]

Hello everyone,

I have a dataset consisting of irregular points in 3D space, each with a 
scalar value associated with them. I am reading this in as a 
vtkUnstructuredGrid, glyphing and rendering and all is fine.  However, I 
wish to concentrate on a certain volume in space and therefore am trying 
to use vtkExtractUnstructuredGrid to filter the output of the data 
reader.  Even with no filtering options switched on, I get no output 
from the filter and see the following debug message:

Debug: In /usr/local/VTK/Graphics/vtkExtractUnstructuredGrid.cxx, line 131
vtkExtractUnstructuredGrid (0x2ec3320): No data to extract!

I would be very grateful if anyone has any suggestions on what I might 
be doing wrong.  I include the relevant bits of my (tcl) script below.

(I am using vtk 5.0.3 under Fedora Core 6 on a dual-core AMD.)

Thanks,

Andrew.

vtkUnstructuredGridReader readerEMIM
   readerEMIM SetFileName $input_file(0)
   readerEMIM SetScalarsName "frame_times"
   # Update the reader object so that it actually reads
   # in the data from the file (otherwise it will do this
   # only when the data is needed
   readerEMIM Update

vtkExtractUnstructuredGrid extractGrid
     extractGrid DebugOn
     extractGrid MergingOff
     extractGrid ExtentClippingOn
     eval extractGrid SetExtent $bounds
     set bounds [extractGrid GetExtent]
     # Check that the bounds have been set correctly
     puts "Bounds in extractGrid are $bounds"
     extractGrid SetInputConnection [readerEMIM GetOutputPort]
     extractGrid Update


-- 

Dr Andrew Porter
School of Chemistry, University of Manchester,
Manchester Interdisciplinary Biocentre,
131 Princess Street,
Manchester, M1 7DN.

e: andrew.porter at manchester.ac.uk
t: +44 (0)161 306 2715