Bidirectional Distancemap for Efficient Volume Ray Casting

摘要

A method using a ray-coherence in volume ray casting skips over transparent region efficiently because a current ray advances as the amount of the leaping distance between an image plane and the object boundary of a representative ray. If the ray jumps over the object boundary, a user-selected constant distance of which the size is larger than the unit distance is commonly used to reach the boundary quickly. However, since we cannot determine an accurate distance, the traversal speed depends on the constant distance. In this paper, to support efficient space-leaping in transparent region and to determine the distance from inside of an object to its boundary, we generate a distancemap for transparent region as well as for nontransparent region, named bidirectional distancemap. In rendering step, a current ray advances as the amount of the leaping distance of a representative ray. If it lies on transparent region, we use our distancemap for transparent region such as the previous approaches. Otherwise, when it already jumps over an object boundary, the distancemap for nontransparent region is exploited.