有限元网格体绘制中的剖切算法

Cutting Algorithm in the Volume Rendering of FEM

为了解决体绘制中的遮挡问题和加快复杂剖切体的剖切操作 ,在 MS体绘制算法的基础上 ,研究和提出了一种体绘制中任意封闭多面体的剖切和多种变换函数 ,并进一步展现了数据场内部的数据分布情况 .另外 ,由于通过二叉树对多剖切体情况下 Stencil参照值的合并 ,使得算法在每一切层上的绘制次数达到最少 ,同时还统一了剖切体前后表面 Stencil操作 ,并减少了不必要的法线运算 。

Volume rendering is a very effectived method to help user to find problems inside a very complicated structure. Compared with surface based visualization methods, it keeps more detail information in the final 2D image. This advantage just brings up another big problem. Usually some important information is obscured or overwhelmed by the data standing closer to the observer. To solve this problem, two algorithms are put forward in this paper. Cutting the structure with an arbitrary convex polyhedron to bring forward the focused part. By using the hardware supported stencil function in OpenGL, the cutting operation become very fast and easy. Another method is the definition of multiple transfer functions. The integration of these two methods makes the user's inspection more flexible. To achieve nearly real time response, several optimization methods are taken in this paper. The rendering time in each slice is decreased to the minimum due to the combination of stencil reference values by using binary tree. The integration of the stencil operations between the front and back faces of polyhedron speed the algorithm greatly by saving lots of complicate normal computations.