Hello,
I’m glad to help. Here’s the role of the view-up vector if I was not very clear:
As you can see, setting only the camera’s focal point (“orientation” in the figure above) and position is not enough to define the viewing geometry. The view-up vector tells the renderer where the “up” of the camera is pointing to. The view-up vector should, under normal circumstances, be orthogonal to the normal vector of viewing plane (the blue panel in the figure). Setting it parallel to the normal would result in ill-conditioned matrices and divisions by zero in the computations down the rendering pipeline. Hence the VTK error.
take care,
Paulo