Scripting Guide - SAS

432 Three-Dimensional Scenes Chapter 13
Setting the Viewing Space
Setting the Viewing Space
3-D scenes can be rendered in two ways. Orthographic projections place the elements in a box, where
coordinates are not changed to accommodate the perspective of the viewer. Perspective projections modify
the display to simulate the position of the elements in relation to the position of the viewer. For example,
two parallel lines (like railroad tracks) stay parallel in orthographic projections, but seem to connect at a
distance in perspective projections.
Figure 13.4 Parallel Lines in an Orthographic Projection(left) and a Perspective Projection (right)
As another example, imagine looking at a tube edge-on (like a telescope). In an orthographic projection, the
tube would appear as a thin circle. In a perspective projection, the circle would have a thickness; the hole at
the far end of the tube would appear smaller than the close hole, and the interior of the tube is visible.
Therefore, the viewable space of an orthographic projection is a rectangular shape, while that of a
perspective projection is the frustum of a pyramid (that is, a pyramid whose top has been sliced off).