多细节层次模型（ LOD）技术已广泛应用于计算机仿真、虚拟现实等多个领域。动车组虚拟现实系统中，由于复杂模型零件个数众多，结构复杂，为了尽可能展示逼真的虚拟场景，运用LOD理念进行模型简化具有重要意义。现有的研究成果多着眼于模型网格和纹理结构的简化，较少考虑模型本身所具有的外部形状特征。本文提出了一种分步式模型简化算法，先通过简化的边折叠方法进行预处理，再运用基于包围盒的AABB算法进一步简化，并且通过引入阈值来控制生成不同精度的模型。实验证明，处理后的模型不但达到了较高的简化率，而且具有较高的真实感。%Level of detail ( LOD) technology is widely used in computer simulation, virtual reality and other fields. In the virtual reality system of electric multiple units ( EMUs) , complex models with complex structures have many spare parts, so simplifying the model by LOD technology is important in showing realistic virtual scenes. Most of re⁃searches currently only focus on simplifying the grid and texture of the model while ignoring the characteristics of the external shape of the model. In this paper, a method to simplify models by fractional steps is proposed. This method contains two steps as follows:the first step is to preprocess the model by the edge collapse method;the sec⁃ond step is to use the axis⁃aligned bounding box ( AABB) algorithm based on bounding box to do further simplifica⁃tion. Different precision models are generated by the introduction of thresholds. The experiment results show that the model which has been processed not only achieves a high simplification rate, but also has high fidelity.
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