[vtkusers] Problems with vtkTkRenderWidget

[Luis Sainz Hermoso]

Hi vtkusers!
	I've done a Tcl script in which you can pick an actor,get the
picked position (in the world coordinate space) and draw an actor at that
point,which is on the surface of the main actor.
	I want to do this with vtkTkRenderWidget and I've tried to modify
the TkInteractor.tcl script, but I have a problem.I've used the Pick
method (as it's done in the TkInteractor.tcl script) instead of using the
GetPickPosition Method and I don't know  the Z coordinate of the surface
of the actor. I've been trying to get the Z component stored in the
Zbuffer using the GetZBufferData method of vtkRenderWindow but it doesn't  
work in Tcl. I think that if I knew this z coordenate it would work, but  
I'm not sure.Does anyone know how can I get the Z component? Am I in the
right way?

	Thanks 

		Luis

P.S I would be grateful if somebody could send me an example