1. The R*-tree an efficient and robust access method for points and rectangles;Beckmann,1990
2. An upper bound for the number of equal nonoverlaping spheres that can touch another of the same size;Coxeter;Symposia in Pure Mathematics,1964
3. A density-based algorithm for discovering clusters in large spatial database with noise;Ester,1996
4. A database interface for clustering in large spatial databases;Ester,1995