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Figure 1: Sample scene consisting of roughly 1.9 million triangles (left). Our method (middle) results in a significant reduction of ray shooting costs compared to a regular bounding volume hierarchy (right). The heat views visualize the summed number of traversal steps and primitive intersections for primary rays. AbstractBounding volume hierarchies (BVH) have become a widely used alternative to kD-trees as the acceleration structure of choice in modern ray tracing systems. However, BVHs adapt poorly to nonuniformly tessellated scenes, which leads to increased ray shooting costs. This paper presents a novel and practical BVH construction algorithm, which addresses the issue by utilizing spatial splitting similar to kD-trees. In contrast to previous preprocessing approaches, our method uses the surface area heuristic to control primitive splitting during tree construction. We show that our algorithm produces significantly more efficient hierarchies than other techniques. In addition, user parameters that directly influence splitting are eliminated, making the algorithm easily controllable.

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Native cellulose samples having a wide range of crystallinity and crystallite size were mercerized by treatment with sodium hydroxide. The resultant cellulose I1 samples showed only a narrow range of crystallinity and an essentially constant crystallite size. For the low-crystallinity samples, crystallinity and crystallite size actually increased on mercerization. These results are in line with the proposal that mercerization involves the mingling of chains from adjacent and antiparallel cellulose I microjbrils to form cellulose I1 crystals of antiparallel chains.

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