基于图象空间判据的地表模型加速绘制技术

在利用图形绘制实现虚拟现实的研究工作中，为了加速图形生成以保证实时的图形绘制，物体层次细节模型LoD(level of detail)的选择是其最主要的解决办法.其主要原理是根据物体对于观察者的重要性选择该物体绘制的细节.地表模型作为多边形网格模型的一种特殊几何模型，在各种虚拟现实系统中有着重要而广泛的应用.该文通过对地表模型实时生成特殊性要求的分析，提出具有焦点加权因子的基于图象空间误差的、适用于地表模型特殊性的、有效的加速简化方法.以焦点和显示面积的有效结合作为物体重要性评价尺度，有效地简化了地表模型的绘制.同时，算法结合均匀网格模型的多分辨率细节层次模型，以“块”作为地表模型大面积简化的空间单位，加速地表模型的简化操作，以实现较为复杂的地表模型的实时绘制.

Accelerating Techniques in Rendering Terrain Surface Based on Image-Space Error

LoD (level of detail) is one of the most important techniques in creating real-time rendering of virtual environment. As a special mesh model, terrain surface model has important and wide-ranged application background in virtual reality. In this paper, the authors present an algorithm for real-time LoD reduction and display of high-complexity terrain surface data. The algorithm allows the generation and computation of appropriate level of detail dynamically by using the compact and efficient regular grid representation. Through analysis of the special requirement for rendering virtual terrain surface, they combine size and focus criteria to estimate the importance of detail of terrain surface and provide a screen-space threshold to bound the maximum error of the projected image. Besides, the whole dataset is constructed into a hierarchy of block-based representations with their error bound precalculated. As a result, a coarse level of simplification could be firstly performed to choose discrete level of detail for the surface mesh, and further simplification is operated on individual mesh vertices within a block. The algorithm has been implemented for approximating and rendering digital terrain models and the experimental results show its high efficiency.