Applying space subdivision techniques to volume rendering

The authors present a ray-tracing algorithm for volume rendering designed to work efficiently when the data of interest is distributed sparsely through the volume. A simple preprocessing step identifies the voxels representing features of interest. Frequently this set of voxels, arbitrarily distributed in three-dimensional space, is a small fraction of the original voxel grid. A median-cut space partitioning scheme, combined with bounding volumes to prune void spaces in the resulting search structure, is used to store the voxels of interest in a k-d tree. The k-d tree is used as a data structure. The tree is then efficiently ray-traced to render the voxel data. The k-d tree is view independent, and can be used for animation sequences involving changes in positions of the viewer or positions of lights. This search structure has been applied to render voxel data from MRI, CAT scan, and electron density distributions