目的 K-D树和Shell常被用于加速等值面光线跟踪法.如果Isovalue保持不变时,Shell方法效率更高,否则Shell方法需要重构Shell,而K-D树方法速度更快.提出一种结合K-D树和Shell的动态等值面光线跟踪方法,其关键是如何实现两者的平稳切换.方法 首先改进基于K-D树的等值面光线跟踪算法,使得该方法在绘制过程中渐进地构建Shell数据结构.在Isovalue发生变化后,首先使用改进的基于K-D树的等值面光线跟踪算法进行绘制,并在绘制过程中渐进地构建新的Shell数据结构,从而平滑地过渡到绘制效率更高的基于Shell的等值面光线跟踪算法.结果 实验中,在Isovalue动态变化时本文方法的效率接近K-D树方法;但用户在进行缩放、旋转等操作时,本文方法能达到Shell方法的速度.实验结果表明本文方法结合了两者的优点.结论 提出了一种快速Isovalue光线跟踪算法,综合运用K-D树和Shell两种数据结构,在Isovalue保持不变和动态变化两者场合都实现了较高的绘制速度.

Objective 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.Method 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.Result 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.Conclusion 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.