基于边界投射与GPU解析的铁路线路LoD网格场景建模方法  

Modeling approach for railway alignment LoD mesh scene based on boundary projection and GPU render

作　　者：陈燕平 宋陶然[1] 孙颖 CHEN Yanping;SONG Taoran;SUN Ying(School of Civil Engineering,Central South University,Changsha 410075,China;China Railway Siyuan Survey and Design Group Co.,Ltd.,Wuhan 430063,China)

机构地区：[1]中南大学土木工程学院,湖南长沙410075 [2]中铁第四勘察设计院集团有限公司,湖北武汉430063

出　　处：《铁道科学与工程学报》2024年第7期2660-2671,共12页Journal of Railway Science and Engineering

基　　金：国家自然科学基金资助项目(52178442)。

摘　　要：层次细节(LoD)网格地形模型是构建铁路线路三维可视化场景的重要基础。然而,受制于LoD网格模型多层次、多尺度表达的复杂动态特征,以及经典LoD四叉树三维网格地形的独立、分块结构形式,在全球数字地形平台上进行铁路线路建模时,地形裁剪开孔、线路地形融合等环节面临诸多难题。对此,提出全球LoD网格地形上基于外边界投射的铁路线路开孔建模方法,以及利用GPU顶点解析的铁路线路LoD地形动态融合叠置方法,从而实现铁路线路LoD网格地形三维场景高效建模。采取GPU与CPU相结合的办法,首先对地形裁剪区域进行过滤,屏蔽区域内的冗余三角形,留下开孔区域,对区域外围顶点通过投射到区域边缘的修正方式实现点位移动以完成边缘填充,从而避免规则网格上的三角网整合建模,实现复杂地形的规则网格兼容表达。然后,在为地形顶点设置全球统一纹理坐标的基础上,在GPU中对地形纹理与叠置图像分别建立不同的纹理坐标转换关系,实现两者的同模无缝表达,其中针对叠置图像的交互,采用仿射变换的方法突破多重空间非线性变换的困难,解决交互时纹理坐标转换的不同步问题。最终,通过某段184 km铁路线路三维建模案例进行有效性验证。研究结果表明:本文方法可对特定地形区域进行开孔裁剪,再利用GPU顶点解析使铁路线路与LoD地形叠置融合,实现外部铁路模型与真实地形的高效融合,铁路大场景三维建模的渲染效率可由40~70帧提升至55~77帧,优化比率约为30%。The LoD(Level of Detail)grid terrain model is an important foundation for building a 3D visual scene of railway alignments.However,due to the complex dynamic characteristics of LoD grid models with multiple levels and scales,as well as the independent and blocky structures of classical LoD quadtree 3D grid terrain,many difficulties are posed for terrain clipping-trepanning.The alignment terrain integration when modeling railway alignments on a global digital terrain platform.To address these issues,this article proposed a trepanning method for railway alignments based on the outer boundary projection on global LoD grid terrain,as well as a dynamic combination and overlay method for railway alignments and LoD terrain using GPU vertex parsing,thereby achieving efficient modeling of 3D scenes of railway alignment LOD grid terrain.Specifically,this paper combined the GPU and CPU methods to filter the terrain clipping area to shield the redundant triangles inside the area and,hence,leaving the trepanning regions.The peripheral vertices were moved to the corrected position on the edge of the area through projection to complete edge filling,thereby avoiding the triangulation integration modeling on regular grid and achieving regular grid compatible expression of terrain.Subsequently,based on setting global unified texture coordinates for terrain vertices,different texture coordinate transformational relationships were established in GPU for terrain texture and overlay image to achieve seamless expression between them.For the interaction of overlay image,affine transformation was adopted to overcome the difficulty of multiple spatial nonlinear transformations and solve the asynchronous problem of texture coordinate conversion during interaction.The effectiveness of the method is verified through a section of 184 km railway alignment 3D modeling case.The results are shown as follows.The method proposed in this paper can clip and modify specific terrain areas.The use of GPU vertex parsing can achieve efficient integration

关 键 词：铁路线路 层次细节模型 地形裁剪 图像叠置 三维可视化 

分 类 号：U212.32[交通运输工程—道路与铁道工程]