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.
维普
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