[6.837] Regarding the up vector

[Hector Briceno <hbriceno@graphics.lcs.mit.edu>]

Hi,
	I remember telling some people in class that the up vector can be
ill-defined when the camara is aligned with it.  This condition is true.

But the up vector is well defined for the initial case or when the applet
is started, therefore it can be well defined after any transformations.

This basically says that you should be able to tilt all the way around and
see the world like if you were doing a flip or sommersault.

For the case of the Mom or Jr Cam, it is also well defined.  Think what
would be the case if you where the lamp.  'up' is well defined in that
case.

I hope I did not cause any confusions.


Hector