[vtkusers] How to convert from Z Buffer values to z values in world coordinates ?

[Deepak Roy]

hello,
   
  This is a question for all the z-buffer experts.
   
  How can i convert the z-buffer values of an offscreen render window back to the z-values in the world coordinate system.
   
  - I am using parallel projection by calling 
   
  vtkRenderer::GetActiveCamera()::ParallelProjectionOn().
   
  - Then I am setting the size of the view port by using vtkRenderWindow::SetSize.
   
  - I rendered one actor and extracted the z-buffer 
   
  - Then i made the first actor invisible and rendered a second actor. Extracted the z-buffer again.
   
  - Now i compute the cumulative difference between the two z-buffers by subtracting the two z-buffers
   
  - I want to transform this difference to the world coordinates. How do i do it ?
   
  - I have no idea how to go about, in doing this backward projection transformation. 
   
  - Please Help !!!! Urgent....
   
  - thanks in advance.
   
  Regards,
   
  Deepak Roy
   
   
   
   
   

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