铁路线路与地形三维模型实时动态融合方法研究

Real-time dynamic merging method of railway alignments and 3D terrain models

铁路线路与地形三维模型的融合是实现铁路线路三维正向设计的瓶颈之一。线路设计过程中,需要实时更新三维场景。现有的静态融合方法会修改原始的地形数据,且计算量大,耗时过长,无法满足动态交互式设计的需求。对此,提出一种铁路线路与地形三维模型实时动态融合方法。基于铁路三维场景,在每帧显示前动态提取视相关地形瓦片模型和线路三维模型,在内存中基于线程池并行对地形瓦片裁剪,实现二者的实时融合,并构建缓存队列,重复利用融合结果。为了提升单块地形瓦片和线路三维模型的融合效率,提出了“超挖-回填”的融合思想。借助高效的三角形空间网格索引,快速删除融合边界内及相交网格涉及到的三角形,虽然“超挖”部分三角形,但避免了繁杂的三角形定位、调整计算。依据超挖三角形外边界和融合边界构建“回填”区域,再采用剪耳法对“回填”区域重构三角网,实现铁路线路与地形三维模型的无缝融合。基于该方法开发了铁路线路三维设计系统,对一条104.9 km铁路案例进行了实验,结果表明:其显示帧率可以保持在35~45 fps,且能够实时更新三维场景。相较于传统的静态融合方法,该方法将长时间的全局模型融合转化为帧前的局部视相关动态融合,减少了线路方案修改时更新的融合数据量及计算量,从而满足了动态交互式设计的需求,提升了三维正向设计的效率。

The merging of railway alignment and terrain three-dimensional(3D)models is one of the most important problems for achieving 3D top-down design of railway alignment.In the process of alignment design,the 3D scene need to be updated in real-time.Nevertheless,the existing merging methods provide a kind of static way for modifying the original terrain data,which is quite inefficient and cannot meet the requirements of dynamic interactive design.In this article,a real-time dynamic method for merging railway alignment and terrain 3D models was proposed.Based on the railway 3D scene,the view relevant terrain tile model and the alignment 3D model were dynamically extracted before each frame.In memory,the terrain tiles were cropped parallelly based on the thread pool to achieve a real-time merging for them.Next,a cache queue was constructed to reuse the merging results.To improve the merging efficiency of a single terrain tile and 3D models of the alignment,the merging idea named“over excavation-backfill”was proposed.By utilizing the technology of efficient triangle spatial grid indexing,triangles involved in the grids which were within or intersect with the merging boundary were quickly deleted.Although some triangles were“over excavated”,complex triangle positioning and adjustment calculations were avoided.“Backfill”area was constructed based on the outer boundary of the“over excavation”triangle and merging boundary.Next,the triangular network of the obtained area was reconstructed by using the ear cutting method,through which the seamless merging of railway alignment and terrain 3D models was achieved.A 3D design system for railway alignment was developed by this method.An experiment was carried out a 104.9 km railway case,and the result showed that the frame rate was at 35~45 fps and the 3D scene can be updated in real-time.Compared with the traditional static merging methods,the dynamic merging method transforms long-term global model merging into local view relevant dynamic merging before the frame,reducing the amount of merging data and computation updated when alignment information is modified.Thereby it can meet the requirements of dynamic interactive design and improving the 3D top-down design efficiency.