An Efficient Parametric Algorithm for Octree Traversal

J.Revelles*, C. Ureña*, M. Lastra**

*Dpt. Lenguajes y Sistemas Informáticos, E.T.S. Ingeniería Informática,

University of Granada, Spain.

e-mail: [jrevelle, almagro]@ugr.es

URL: http://giig.ugr.es

** Dpt. Informática, E.U.P. Linares,

University of Jaén, Spain.

e-mail: mlastral@ujaen.es

ABSTRACT

An octree is a well known hierarchical spatial structure which is widely used in Computer Graphics algorithms. One of the most frequent operations is the computation of the octree voxels intersected by a straight line. This has a number of applications, such as ray-object intersection tests speed-up and visualisation of hierarchical density models by ray-casting. Several methods have been proposed to achieve this goal, which differ in the order in which intersected voxels are visited. In this paper we introduce a new top-down parametric method. The main difference with previously proposed methods is related to descent movements, that is, the selection of a child sub-voxel from the current one. This selection, as the algorithm, is based on the parameter of the ray and comprises simple comparisons. The resulting algorithm is easy to implement, and efficient when compared to other related top-down and bottom-up algorithms for octrees. Finally, a comparison with Kelvin's method for binary trees is presented.

Keywords: Octree, Binary tree, Ray Tracing, Acceleration Techniques.