Issue No. 07 - July (2009 vol. 31)

ISSN: 0162-8828

pp: 1178-1183

Shojiro Tanaka , Shimane University, Matsue

Kunio Aizawa , Shimane University, Matsue

ABSTRACT

Quadtrees and linear quadtrees are well-known hierarchical data structures to represent square images of size 2^{r} \times 2^{r}. Finding the neighbors of a specific leaf node is a fundamental operation for many algorithms that manipulate quadtree data structures. In quadtrees, finding neighbors takes O(r) computational time for the worst case, where r is the resolution (or height) of a given quadtree. Schrack [1] proposed a constant-time algorithm for finding equal-sized neighbors in linear quadtrees. His algorithm calculates the location codes of equal-sized neighbors; it says nothing, however, about their existence. To ensure their existence, additional checking of the location codes is needed, which usually takes O(r) computational time. In this paper, a new algorithm to find the neighbors of a given leaf node in a quadtree is proposed which requires just O(1) (i.e., constant) computational time for the worst case. Moreover, the algorithm takes no notice of the existence or nonexistence of neighbors. Thus, no additional checking is needed. The new algorithm will greatly reduce the computational complexities of almost all algorithms based on quadtrees.

INDEX TERMS

Image processing, quadtrees, linear quadtrees, neighbor finding.

CITATION

Shojiro Tanaka, Kunio Aizawa, "A Constant-Time Algorithm for Finding Neighbors in Quadtrees",

*IEEE Transactions on Pattern Analysis & Machine Intelligence*, vol. 31, no. , pp. 1178-1183, July 2009, doi:10.1109/TPAMI.2008.145