Forcing rendering

Dear All,

I do the rendering of several volumes in same 3D image.
Some of them are over the others and shadow the previous rendered ones.
How I force re-render the previous ones (volumes) to appear the shadowed areas? (and to shadow the new ones areas instead)
I tried to do the following (to the previous ones). I added again the volume (the volumeMapper and volume was not reallocated but used the previous allocation)

    volumeMapper.SetInputConnection(reader.GetOutputPort())
    renderer.AddVolume(volume)
    renderWindow.Render()

But the new volumes remains over the old ones (previous ones) contrary to what I want.

Thanks,

Luís Gonçalves

renderer.RemoveVolume(volume)

And re-render the previous volume again.