[vtkusers] vtkCommand calldata parameter of Execute()

[Luke]

Hello,
  I'm would like to make an animation similar to this one:
http://www.vtk.org/Wiki/VTK/Examples/Cxx/Utilities/Animation

but I would like to pass the information about the position and
orientation of the actors in my scene at each render time as the third
argument to Execute.  In the above example this parameter isn't used,
and I was unable to determine from the documentation of vtkCommand or
vtkRenderWindowInteractor how to pass this data when the timer event
occurs.

Does anybody have a good example of a callback that gets data passed to it?

Thanks,
~Luke