Parts based on some of the below images:
http://en.wikipedia.org/wiki/File:Zentralperspektive.png
http://en.wikipedia.org/wiki/File:Cavalier_perspective_45.svg
http://en.wikipedia.org/wiki/File:Ray_trace_diagram.svg
http://www.labsafety.com/refinfo/ezfacts/ezf118.htm

Most is copyright by Michalis Kamburelis, reuse on terms of GNU GPL >= 2.