> Links:
> Basics, demo and implementations: http://en.wikipedia.org/wiki/R*_tree
> SQLite: http://www.sqlite.org/rtree.html
> Theory: http://epub.ub.uni-muenchen.de/4256/1/31.pdf
> GiST: http://gist.cs.berkeley.edu/
>

see also :
Ingres R-Tree Detailed Design Specification
http://community.ingres.com/w/files/d/d1/Ingres_Rtree_DDS.pdf