Extraction And Reconstruction Of Indoor Space Structure Model Based On BIM

With the development of urbanization,the construction of digital city and smart city requires more refined and rapidly modeled indoor space model data.On the one hand,the measurement,acquisition and modeling of the indoor three-dimensional structure has difficulty in data acquisition and its automation of modeling is at a low degree.On the other hand,in the field of building information,the building information model(BIM)has become widely recognized as a modeling tool in the industry and it provides an indoor spatial data carrier with rich semantic and geometric information.How to integrate and utilize it in the area of GIS which is seen as the most suitable platform of smart city,has become a hot research topic and urgent application demand.At present,due to the complexity of the indoor environment and the difficulty of acquisiting indoor data with semantic and geometrical information,it is not easy to express and refine the modeling of indoor objects.Many scholars use BIM as a data source to extract the semantic and geometric information of buildings and transform them into GIS models to support the research of GIS indoor space.However,most scholars use CityGML as the carrier of the indoor model to express the indoor environment.Due to the defects of CityGML itself,for example lacking the expression of indoor connectivity,it is hard to satisfy some three-dimensional application such as indoor fireworks diffusion and gas diffusion.In view of the above problems,this paper extracts the building information of LOD4 level by analyzing the BIM model and transforming the information into the CityGML model.After that,the indoor topology information is constructed by combining the IndoorGML model with CityGML.The research content of this paper mainly includes the following points:(1)Extraction and transformation of semantic and geometric information of BIM modelsThe BIM model is mainly used for the design,construction and management of the whole life cycle of the building.It contains detailed and rich architectural geometry and semantic information.However,BIM doesn't has the capability of GIS analysis.So there is a necessity to extract and convert these information to the GIS platform.In this paper,the three geometric representations:SweptSolid,CSG and Brep in BIM model,are extracted,and their parameterized expressions are uniformly converted into Brep expressions in CityGML.Besides,semantics in BIM model are filtered according to CityGML LOD4 criterior to build a complete GIS building model.(2)Construction of indoor topologyBased on the transformed model,this paper combines the IndoorGML model to construct an indoor two-dimensional connected network,which provides data for indoor navigation,path analysis and other applications.When building a connected network,this article filters out objects that are not navigable indoors,such as furniture,leaving only rooms,corridors,stairs,and doors.The connectivity between them is determined by their spatial positional relationship with each other.(3)Division of indoor spaceWhen constructing a network relation graph of an indoor environment,it is necessary to convert the space of the research object into a two-dimensional object and take the center point of the body space as a node.However,due to the diversity of the indoor environment and the complexity of the geometry of the building,a single node in 2D network cannot reasonably describe the indoor environment.Therefore,it is necessary to redivide these objects and construct reasonable connectivity.This paper builds a new topology network for irregular building objects,such as corridors and stairs,by extracting the centerline of the object and rejudging the relationship between the associated objects.In order to meet complex 3DGIS application's requirements,such as indoor gas diffusion,the octree is used to divide the indoor space and each divided space is interconnected by an octree index to provide theoretical basis for complex GIS applications.In this paper,the model data from BIM official website is used for verification.The research results show that the geometric extraction and transformation of BIM model can meet the requirements of CityGML LOD4 level,and can provide complete semantic information.The constructed indoor connected network meets the actual navigation requirements and can be converted to the IndoorGML model;the use of octrees to divide the indoor space can cover the entire indoor space,thus supporting the further in-depth application research.