We now introduce the concept of an observer. Our eventual aim is to represent, in the graphics viewport, a three-dimensional scene as viewed by a person standing at a given position and looking in a given direction; with position and direction specified relative to the ABSOLUTE system. Imagine someone having a graphics screen fixed firmly in front of their face, and as they walk, run, jump, fly, somersault through space, they can only view that space through the screen. It is these images that we will simulate on the graphics viewport, so that the observer sitting comfortably in front of the screen can experience the same sights as our energetic ‘space-traveller’.