[vtkusers] camera->SetViewUp method

[francesco caruso]

hello

i have doubt about this method...

what's the meaning of "up direction for the camera" ?

	
  	  y
    	  ^
    	  |
           |
           |---->x              z direction is outgoing the monitor


if my camera is normal to the plane xy, z direction is outgoing from 
the monitor, camera position is (0,0,100) and camera's focal point is 
(0,0,0)

how have I to set ViewUp ?

thanks in advance

francesco