Research On The Key Technology Of BIM Modle Visualization For Web AR

In the field of architectural design,design drawings are the main communication medium for buildings in different steps.However,due to the limited visual information that the drawings can convey,it is very easy to cause problems of improper communication.The building information model(BIM:Building Information Modeling)composed of building components came into being,it plays an important role in replacing drawings as a construction medium for architectural design institutes and construction sites.Among them,IFC(Industry Foundation Classes),a unified standard for the construction industry,often relies on computers equipped with professional modeling software such as Revit for visualization,which is poor in portability and high in cost.Compared with the existing visualization methods,the implementation based on Web AR can have the advantages of strong cross-platform compatibility,high degree of lightweight,high degree of reality,and strong interactivity.This thesis proposes a BIM model visualization technology,designs and implements a BIM model visualization system for Web AR.The main innovation content has the following three aspects:1)Model structure conversion and building information export.In view of the large difference between the IFC model structure and the model structure supported by commonly used rendering engines and the problem that the building attribute information in the IFC model cannot be converted,this thesis proposes an IFC-based model format conversion technology to convert the IFC model to GLTF format,which is supported by the common rendering engine,and convert the building attribute information into JSON format.2)Model lightweight processing.The BIM model often composed of complex building groups,the model high in precision,and the large amount of data,which causes the problems of high loading time,high pressure of real-time display and rendering.To solve these problems,this thesis proposes a model lightweight scheme,including model culling based on optimal view and model compression.Among them,model culling based on Octree and Z-pyramid culls models that are not in the field of view and model blocks that are completely occluded,reducing the amount of model data required for the first loading of the Web.Model compression is based on Draco and MeshOpt model compression algorithms to reduce the amount of model data from quantization,mesh compression and other aspects.3)Progressive loading scheme.Aiming at the characteristics of large model building space and limited model structure in the field of view in BIM model visualization,this thesis proposes a progressive BIM model loading scheme.The remaining models are loaded progressively,in blocks,and multi-threaded according to changes in the field of view,and combined with the browser database for local storage to avoid repeated loading of model blocks.Among them,based on KD Tree nearest neighbor search this thesis proposes a model block method that divides the large BIM model into small model blocks,and outputs a list of small model blocks with spatial proximity and data uniformity.Combined with Web multithreading technology,the visible model block list is loaded and rendered in parallel.Based on the above three innovative research contents,this thesis designs and implements a Web AR-oriented BIM model visualization system,and tests the functions and performance of the system.Tests show that the prototype system can meet the basic requirements of BIM model visualization in the architectural field.