The projection type element is a numeric variable determining the mode of the scene projection onto a 3D window:

 

0 perspective projection (default)

1 ortographic projection

2 perspective projection, right-handed coordinate system

3 ortographic projection, right-handed coordinate system

 

The 0 and 1 projection types are projections of the left-handed coordinate system (default coordinate system), the 2 and 3 projection types are projections of the right-handed coordinate system (the Z-axis pointing in the opposite direction, and the rotations having the opposite directions). The newly created objects are accommodated to the right-handed coordinate system (this does not hold for objects read from a file or a text), therefore the right-handed coordinate system should be activated before some object is created. For the right-handed coordinate system it is necessary to correct the Z coordinate of the default camera (to change it from -2 to 2), as well as to change the default lighting rotation (the Y rotation from +45 degrees to -45 degrees, the X rotation from +45 degrees to +135 degrees).

 

The 0 and 2 projections are perspective projections. The object gets diminished with increasing distance. The 1 and 3 projections are orthographic projections. The object size does not depend on distance. The orthographic projection is used for engineering purposes (machine drawings, CAD programs). In the orthographic projection the scale of the scene display can be controlled by the camera scale adjustment.