[vtkusers] Initialize visualization pipeline

[Laurent PAUL]

Hi users,

I created a 3D viewer.
I have a problem when initializing the pipeline. I build a 3D window with
mapper, renderer...
The problem is when I build this pipeline, reader is not ready since it
hasn't any directory (I use vtkDicomImageReader).
So, VTK complains that "vtkVolumeRayCastmapper has 0 connections but is
not optional".
So far, I initialized reader with a black 2D image, but I don't think it
is a good solution.

How can I initialize pipeline to avoid the vtkOutputWindow error?

Thanks,

Laurent.