great work, i have been working on the rotation of a camera, and i was going to get on to the frustum.
i want to make a 3dsmax sort of way of moving camera in openframeworks, anyway thought it might be useful,
however it is in no way finnish, and i now have much nicer code function, but i does not plug in to the camera yet.
but this is sort of how it will work.
also you might like my camera tweener add-on for tweening between ofeasyCam