| As concepts such as Digital China and Smart City continue to be put forward,spatial data has attracted attention from all walks of life,and the demand for digitalization and informatization of cities continues to increase.Geographic Information System(GIS)is a spatial database technology serving geographic information.It has powerful capabilities for analyzing,managing,querying and visualizing spatial data in two or three dimensions;Building Information Model(BIM)is a digital expression of building infrastructure,including all the information data of the whole life cycle of the building.GIS will make up for BIM's lack of macro environment,and will also promote the application of BIM from the refined single model design to the level of multidimensional spatial data;at the same time,high-precision BIM will become an important source of microscopic data for GIS;The integration of BIM and GIS will complement each other and lay a foundation for the construction of smart city.However,due to the characteristics of BIM,such as complex data structure and large amount of data information,with the condition of limited hardware resources,visualizing large-scale BIM and GIS data is still a challenging task,especially on the Web and mobile terminals.Aiming at the difficulty of simultaneously loading and rendering large-scale GIS data and large-scale BIM data in the Web system,this paper proposes a visualization method based on the fusion of multi-level of detail GIS+BIM hybrid model.This method over-divides GIS and BIM data from macro to micro and establishes a 4-layer spatial structure hierarchy,combined with external contour extraction algorithms and other technologies to obtain sub-models at each level,and finally chooses 3D Tiles that are more suitable for rendering large-scale spatial data on the Web as an integrated container of BIM and GIS data,while ensuring the integrity of BIM data information,it also enables the efficient and rapid rendering of GIS and BIM models on the Web side.The main research contents and achievements include:(1)Analyze and study WebGL technology,on this basis,deeply study the visualization function of Cesium open source library,according to the current BIM model actual application scenarios,combined with the needs of the subject to flexibly apply and develop,and formulated the overall structure framework of the visualization system,targeted rendering performance optimization.(2)In view of the huge volume of BIM model and the complex data structure,this paper applies the method of dividing the detail level of architectural model in the City Geography Markup Language standard to the BIM model.Combined with the contour extraction algorithm and the class component set extraction method,the BIM model is decomposed into rough outer contour,fine outer contour and indoor facility three-layer sub-model,and corresponding sub-model files are obtained to provide data support for dynamic scheduling of subsequent models.(3)Aiming at the problem of too simple description of buildings in the field of GIS and the lack of micro-data information,this paper proposes a visualization method that integrates macro-GIS models and micro-BIM models,customizes and builds a GIS+BIM hybrid data structure,and integrates the same building the multi-level transition model of GIS white mold and BIM forms a visualization effect from macro to micro,GIS to BIM,and rough to fine,which will improve the visualization rendering efficiency of large-scale GIS+BIM data.(4)In order to improve the network transmission speed of model data,this article uses 3D Tiles as an intermediate container for integrating BIM and GIS,converts all model data into the 3D Tile data format that can be efficiently and quickly rendered on the web,and designs the spatial index of 3D Tile data to reasonably organize model tiles with different fineness,and realizes dynamic rendering scheduling of 3D Tile data based on the change of line-of-view,so as to reduce the rendering burden of the browser model.(5)Designed and developed a 3D spatial data visualization system based on the Cesium digital earth engine,including interactive function modules such as information query,model positioning,distance measurement,route roaming,component hiding,and model movement;finally,the feasibility of this method was verified through experimental analysis.This method can effectively alleviate the problem of rendering large-scale BIM and GIS models with limited hardware resources,and achieve the expected effect of improving the visualization efficiency of GIS + BIM scenes. |
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