| Distance of Projection Plane|
By means of the distance of projection plane element the distance of the plane can be determined on which the scene being displayed is projected. The projection plane distance specifies how large portion of the scene is supposed to be displayed. The default setting of this distance is 1. When the projection plane gets more distant, the cut-out of the scene displayed gets smaller. Thus a zoom scene effect (a telescope function) may be created. When the projection plane gets nearer, the cut-out of the scene displayed gets larger. Thus the fish-eye effect may be created. The projection plane distance may not be <= 0.
For the projection plane it holds that objects the distance of which equals that of the projection plane are displayed in the unity magnitude. The unity magnitude is (3D_window_width + 3D_window_height)/2. For a square 3D window a wall sized 1x1 and lying in the projection plane will fill out exactly the entire 3D window area.
In the 3D window objects having their minimum distance equal to 1/4 of the projection plane distance will be displayed. The maximum distance for displaying objects equals the visual range distance
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