[vtkusers] Smooth surfaces of *.pvtp datasets?

[Christoph Moder]

Hi all!

I want to generate a movie from a series of *.pvtp files. Therefore,
I've written a script that reads the input files, renders them and
generates a *.png image. But the surface does not look smooth; one can
recognize the individual diamond-shaped *.vtp pieces.
http://christoph-moder.de/download/temp/vtkusers/image_movie_step001_small.png

This does not happen when I load the files into Paraview; there I have
an absolutely smooth surface. So what's wrong?
http://christoph-moder.de/download/temp/vtkusers/image_movie_step001_paraview_small.png

My vtk script:
http://christoph-moder.de/download/temp/vtkusers/generate_image_vtkusers.tcl

Thanks!
Christoph