Abstract: Volumetric features representation plays a vital role for user understanding and recognizing the virtual environment. The current algorithm is inefficient due to its large storage and inconvenient acceleration in GPU, and it is difficult to satisfy the real-time requirements of visualization. Aiming at this problem, an efficient volumetric features representation algorithm using heightfields-octree is proposed. The algorithm can not only solve the problem that the heightfields can only represent 2.5 dimensional scene, and cannot express the true 3 dimensional scene, but also provide a new feasible way for volumetric features representation. The heightfields representation of 3D scene is generated by octree structure, which extends the traditional heightfields of z to x, y and z three directions. Firstly, a preprocessing method of triangular is put forward, ensuring model accuracy and data integrity. Secondly, an algorithm of heightfields judgment and rasterization on projection transformation is proposed, converting geometric primitives into heightfields of two-dimensional space. Finally, the ray casting algorithm based on heightfields octree is realized. The experimental results show that the algorithm can dramatically reduce data storage capacity, and higher ray casting efficiency, and better expression of 3 dimensional scene.

Key words: volumetric features representation, heightfields-octree, projection transformation, ray casting

摘要： 体特征表达对用户理解和认知虚拟环境有着至关重要的作用。当前的体特征表达算法由于存储量大且不易于在GPU中加速等问题，渲染效率低下，难以满足场景可视化的实时性需求。针对这一问题，提出了一种高效的高度场八叉树体特征表达算法，不仅解决了传统高度场仅能表达2.5维模型，无法表达真三维模型的问题，而且为体特征表达提供了一种新的可行途径。算法使用八叉树结构生成三维模型的高度场表示，将传统的z向高度场扩展到x，y，z三个方向的高度场。首先，提出了三角面片预处理方法，保证模型精度和数据的完整性;其次，提出了基于投影变换的高度场表示判断及栅格化方法，将几何图元转换成二维空间的高度场数据;最后，提出了基于高度场八叉树的光线投射算法。实验结果表明，算法能极大地减少存储量，具有较高的光线投射效率，表达三维模型时取得较好效果。

关键词: 体特征表达, 高度场八叉树, 投影变换, 光线投射