PR Quadtree Demo
Recursively decompose the underlying space into four equal area blocks
until each block contains at most one data point. The partition positions
are independent of the data.
details, see pages 42-47 and 758-761 of Samet,
Foundations of Multidimensional and Metric Data Structures
or, see pages 102-103 of Samet,
Design and Analysis of Spatial Data Structures.