### 3.7.192. Quadtree

Denotes the fact that, for a given constraint, a quadtree can be used within its filtering algorithm. A quadtree is a hierarchical data structure based on the recursive decomposition of space. Figure 3.7.43 illustrates the representation of a two -dimensional binary region (A) with a quadtree (C). A region is subdivised into quadrants, subquadrants, and so on (B), until blocks consist entirely of 1s or entirely of 0s.