3.3.5 Normal Screen Co-ordinate System

The normal screen coordinate system takes a picture of a view that is currently represented in the view coordinate system to place that view on a two-dimensional screen in much the same way as a camera takes a picture of a view to record that view on film. In other words, the normal screen coordinate system converts a 3D volume into a 2D screen by applying conversion algorithms. By using perspective transformation calculations, the conversion process ensures that objects that are far away appear small.

The normal screen coordinate system converts the 3D view volume of the rectangular pyramid in the view coordinate system into a 2D rectangle. For example, this view:

is converted into this screen:

The normal screen coordinate system is the display equipment for the virtual 3D space inside your computer. As with the view coordinate system, the viewing direction is the Z-axis and the center of the screen is the origin.

Coordinates in the normal screen coordinate system are expressed as (x_s,y_s,z_s).