Let me semi-address your question of references. The trick is that I'm not aware of much "new" that pertains to the problem. The speed issue of UG and RQT is solely an implementation detail related to being cache obvious. Back when I had anything to do with academia (and dinosaurs walked the earth) the references were by Hanan Samet
. You're probably better off just spending some time on citeseer
. You kids today have no idea how lucky you are to have free access to tons of research papers. A quick search yielded this http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.148.4652
which appears (from a 2 minute skim of 160 page paper) to be a reasonable to get an overview of some various methods.