| With the popularization of BIM(Building Information Modeling)and the vigorous support of national policies,BIM has been playing an indispensable role in large-scale construction projects by its advantages of improved design efficiency and standardized project management.Revit software of BIM system is widely used in China's construction industry.As a design-editing software for modeling,Revit can be installed and process 3d building model on local PC,and it has high requirements for hardware configuration.However,The Revit models are not only used in the architectural design stage,but also has important application value in project display,construction,supervision and later property management and maintenance.Therefore,the research and development of Web lightweight display function based on Revit model has a broad application prospect and excellent application value in the construction of Intelligent Community and Smart City.At present,there are not many individual researchers in lightweight Revit model presentation,most of them are mature enterprise-level applications,including the Autodesk360 cloud platform released by Autodesk,which developed Revit software,and the BIMFACE lightweight engine developed by the domestic guanglian company.But the Revit exported model is not well compressed and LOD simplification.The Compression model can improve the efficiency of network transmission and reduce the bandwidth pressure,if the model is not simplified,the efficiency of rendering on the Web will be extremely slow for the performance.Therefore,LOD technology in computer graphics is used to realize the multi-resolution detail level model display of Revit model.The main point of this paper is to improve the compression efficiency of the exported model as much as possible and to use the grid simplification algorithm to simplify the model.The difficulty is to restructure the model and add LOD elements,which are used to solve the problem of displaying LOD model on the Web.Therefore,this paper mainly does the following work :(1)Reconstruct Revit model and exporte data structure.(2)Complete the plug-in based on Revit API to export the 3d model into JSON intermediate format.(3)Model compression was carried out in various ways during the export process,including controlling the precision of model export,using hash table to complete repetitive compression,and ZIP compression of JSON file.(4)Research and use grid simplification algorithm to simplify the model in the process of exporting,update the multi-resolution hierarchical structure of the exported data structure to storage model,so as to realize LOD display of the model.Due to the large volume of Revit model,a large amount of simplification time is needed,so an improved algorithm based on edge collapse algorithm is proposed to improve the simplification efficiency of large-scale model.(5)Modify the source code of the three.js model loader,realize the loading and parsing of ZIP file and the improved LOD model structure.Finally realize the efficient and fast rendering of Revit model on the page end by combining the LOD technology of graphics,the simplification technology of the model,and the compression technology.After implementing and optimizing the solution mentioned above,this paper successfully solved the existing problems in Revit model visualization on web side,and enhanced the efficiency of the display and performance,meanwhile the users' browsing speed and experience has improved.Validation of the function and comparison between the effects before and after the solution both illustrated that the designed function is reasonable.The system can be used in the construction and maintenance of the project,as well as in the demonstration,communication and archiving of the model. |
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