B. Praveen Kumar, Phalguni Gupta, C. Jinshong Hwang. A Variation of Quadtree. In M. H. Hamza, editor, Proceedings of the IASTED International Conference on Visualization, Imaging and Image Processing (VIIP 2001), Marbella, Spain, September 3-5, 2001. pages 354-360, ACTA Press, 2001.