The Camera - Essentials of Interactive Computer Graphics - page 369

govern objects' visibility, size, clarity, and so on in the final photograph. For
example, a book behind my camera and a person a mile away from my viewing
direction will reflect light energy toward the camera. However, the physics of
the real world governs that the reflected energy from the topic cannot arrive at the
camera lens, and the reflected energy from the person that is too far away would be
scattered and/or otherwise attenuated before it arrived at the camera lens. In this
way, although both objects participated by reflecting energy toward the camera,
neither will show up in the final photograph. In computer graphics, with limited
computation resources and representation precision, we define a finite volume,
a visible volume , to bound the simulation computation. As the name suggests,
all objects within this finite volume will participate in the rendering process and
thus may be visible in the final image. All objects outside of this volume will be
clipped away and thus cannot participate in the rendering process and will not be
visible in the final image.

14.2.1 Orthographic Projection: A Rectangular Visible Volume

Figure 14.7 illustrates an intuitive way to define a visible volume with respect to
the camera parameters. In this case, a rectangular volume with the dimension of:

width × height × depth = W × H × ( f − n )

Figure 14.7. The rectangular visible volume.