http://www.hl2world.com/
http://www.hl2world.com/wiki/index.php/Main_Page
http://www.cs.unc.edu/~geom/collide/index.shtml
http://en.wikipedia.org/wiki/Axis-aligned_bounding_box
http://en.wikipedia.org/wiki/Collision_detection
Sweep-and-Prune method
http://parallel.vub.ac.be/documentation/pvm/Example/Marc_Ramaekers/node3.html
http://www.ce.chalmers.se/edu/course/EDA425/lectures/colldet.pdf