[vtkusers] Update on ContourFilter

[Andrew Usher]

Hi,

I'm trying to get a contour filter to update within a loop but keep
getting the error:

>> ERROR: In /usr/local/VTK-4.2.2/Graphics/vtkPolyDataNormals.cxx, line 88
>> vtkPolyDataNormals (0x805bc48): No data to generate normals for!

with the code:

  for (int ii=1; ii<5; ii++)
  {
    cntrFilter->GenerateValues(ii, range);
    renWin->Render();
  }

This is a trivial example but I just wondered how to do this. I've tried
to use cntrFilter->ReleaseDataFlagOff(); but with the same error.

I've used cntrFilter->SetInput(myData) earlier in my code which has
produced a rendering as expected but it's just when I try to repeat the
call to GenerateValues() and I thought someone will have done something
similar before, such as an animation?

Thanks very much,

Andrew