[vtkusers] How to add an overlay renderer?

[sercani]

Hi everyone;
I need to add an overlay renderer over the renderer of vtkImageViewer2 
but i couldn't do that...I need this renderer because when the slice 
orientation of vtkImageViewer2 is different than 2,the active camera's 
transform is also changed, so when i want to add a viewprop(for example 
vtkImageActor) on top of the vtkImageViewer2, it isn't be seen...The 
renderwindow contains a vtkCornerAnnotation, a vtkLegendScaleActor and a 
vtkImageViewer2...So how can i add an overlay renderer on top of all of 
these stuff ?...
Sercani....