We will find that it is much more useful to reorient the entire scene such that the camera is located at the origin. Moreover, if we align the scene so that its optical axis (the direction it is looking) is along one of the coordinate axes and twist the scene so that the desired up direction is aligned with our camera's up direction we can greatly simplify the clipping and projection steps that follow.

Once more, the mechanics of this specification can be expressed using the rigid body transformations discussed before. First, we need to perform the rotations needed to align the two coordinate frames.