K-D tree and Shell are commonly utilized to accelerate isosurface ray tracing. Shell-based isovalue ray tracing method is more efficient than K-D treeis if the isovalue is fixed. Otherwise

the K-D tree-based isovalue ray tracing method is more efficient because the shell-based isovalue ray tracing method needs to reconstruct the shell. To utilize the advantages of both methods

this paper presents a fast isovalue ray tracing method by combining K-D tree and Shell. The main point of the proposed method is how to switch between the two methods smoothly. The K-D tree-based isovalue ray-tracing method is first improved to allow a progressive construction of the shell during rendering. The improved K-D tree-based isovalue ray tracing method is used when the isovalue changes

and a new shell is progressively constructed to allow the switch to a faster shell-based isovalue ray-tracing method. The presented method and K-D tree-based isovalue ray tracing method have similar speed when the isovalue changes frequently. The presented method can also achieve a similar speed as that of shell-based isovalue ray tracing method when only the zoom in/zoom out/rotation operation is performed by the user. Result shows that the presented method combines the advantages of both methods. The presented fast isovalue ray tracing method utilizes both K-D tree and Shell and thus can achieve a high rendering speed for fixed isovalue scene and dynamic isovalue scene.