[vtkusers] problems with camera controll

[furlanis at ele.uri.edu]

vtk Users,

I want the users of my program to be able to enter coordinates, and be able to
place the camera there. right now im using a running-total for the azimuth,
elevation, and roll. the Only problem is that im getting errors when i enter an
elevation of +/- 90 degrees.

here's what i got: 

initial position: 0 0 1
focal point: 0 0 0
initial view plane up: 0 1 0

then i have a scale bar that goes from -90 to +90. here's the error message when
it reaches +/-(88-90):

Warning: In /usr/local/vtk/VTK/Rendering/vtkRenderer.cxx, line 775
vtkOpenGLRenderer (0x80f76a0): Resetting view-up since view plane normal is parallel

is there a way i can turn this warning off? or reset the view plane in a way
that wont make my camera turn in a different direction? Neither book (text or
user guide) details the use of the camera, just its concepts. i understand that
the error tells me that my camera is looking parallel with the 'view-up' and
that the renderer can't draw the object because of it, but i dont know how to
fix it, or ignore it.

please help.
-Stephen Furlani