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Item A Survey on Exploiting Grids for Ray Tracing(The Eurographics Association, 2008) Cosenza, Biagio; Vittorio Scarano and Rosario De Chiara and Ugo ErraGrid is one of the first data structure introduced at the very beginning of computer graphics. Grids are used in several applications of computer graphics, especially in rendering algorithms. Lately, in ray tracing dynamic scenes, grid has received attention for its appealing linear time building time. In this paper, we aim to survey several aspects behind the use of grids in ray tracing. In particular we investigate grid traversal algorithms, building techniques and several approaches for hierarchical grids.Item On Estimating the Effectiveness of Temporal and Spatial Coherence in Parallel Ray Tracing(The Eurographics Association, 2008) Cosenza, Biagio; Cordasco, Gennaro; Chiara, Rosario De; Erra, Ugo; Scarano, Vittorio; Vittorio Scarano and Rosario De Chiara and Ugo ErraIn this paper we estimate the effectiveness of exploiting coherence in Parallel Ray Tracing. We present a load- balancing technique which divides the original rendering problem in balanced subtasks and distribute them to independent processors through a Prediction Binary Tree (PBT). Furthermore the PBT allows to exploit temporal coherence among successive image frames. At each new frame, it updates the current PBT using a cost function which uses the previous rendering time as cost estimate. We also provide two heuristics which take advantage of data-locality. We assess the effectiveness of the proposed solution by running two experiments. The £rst one aims to investigate the accurancy of predictions made using the PBT. Results show that such predictions are quite accurate even considering a heavily unbalanced scene and a fast moving camera. The second experiment evaluates the two locality-aware heuristics showing a modest improvement.