Research On The Topological Model Of 3D Building

City is the mostly densely populated area of population,economy,technology,infrastructure and information.With the rapid development of economy,urbanization will become the most important process of economic development in the century.Since Gore put forward the concept of "Digital Earth" at the annual conference of Open GIS Consortium in 1998,the Earth's digital information has been widely discussed in the world.Digital city as the core of digital earth network system,is the key and difficulty of digital earth technology system.The 3D city model is a three-dimensional computer model for urban description,which has become one of the core contents of digital city spatial framework data.Based on the development of software and hardware,many cities and regions have carried out the city three-dimensional modeling and application work,urban three-dimensional model construction has developed from the initial exploration stage to the field of depth and range.As the urban element closely related to human life,building is the research focus of spatial relationships and spatial analysis.Topology as one of spatial relationships has played the underlying role in spatial operations,queries and analysis.Topological relationships indicate the invariant characteristics under topological transformation of the referenced objects,such as adjacent and connected relationships between spatial objects.In many 3D applications,topological relationships are widely discussed in data validation,spatial analysis and visualization,which has introduced a great necessity and importance for representing topological relationships in 3D city models.3D city models in the past focused on visual graphics and geometric information,neglecting the representation of semantics and topology.As a consequence,these models could not satisfy the constantly increasing need for thematic query,spatial analysis and data mining.Besides,the three-dimensional city model of the provider and the user is usually different,leading to the varity of the three-dimensional city model format.As an international standard of the Open Geospatial Consortium(OGC)for the representation and the exchange of 3D city models,CityGML shows its merit in geometrical,semantic and visual representation of 3D city models.With respect to modeling topology,CityGML represents topological relationships through the concept of XLink,which is implemented through referencing the shared object between features.This mechanism is simple and flexible,but it is limited to the features or the geometries which have a shared part.As the standard of BIM,IFC describe spatial relationships between building elements through the inverse attributes on a corse granularity.Based on the fact that CityGML and IFC cannot describe the the topological relations between features and the details of the intersection explicitly,this paper presents a two-level topological model for features in 3D models of building.The related research focuses on the following aspects:(1)Based on the theory of classical four-intersection and nine-intersection model,we compare the types of topological relationships in different models.Five topological relationships(touch,in,overlap,equal and disjoint)are adopted for representing the spatial relationships between buildings(both the geometric primitives and building elements).Ten cases of topological relationships between geometric primitives(point,edge,face and solid)are summarized and discussed.The types of topological relationships between semantic features are determined according to the consistency rules of semantic features.(2)According to the defined topological relationships in 3D models of building,we propose a two-level topological model for features in 3D building.On the bottom level,four kinds of topological primitives are designed for describing topological details.On the top level,five topological relationships are adopted for the spatial relationships between both geometric geometries and semantic features in 3D building.Topological relationships are incorporated in the framework of CityGML in a formal way by means of the ADE approach.This TopoADE consists of three modules:Topology,Feature and Geometry,which supplys a gap of the existing coarse-grained topoligcal representation in XLink.(3)Through analysizing the framework and data structure of CityGML,we define the extended consistency rules in 3D building based on the research on three-dimensional spatial validation and consistency rules for 3D city models.The extended consistency rules can gurantee the accuracy and efficiency of operations in the process of modelling,data validation and spatial analysis,etc.Aiming at various possible cases of invalidation,the methods of repairing surface geometry and solid geometry are proposed.Furthermore,the cases of inconsistent semantic features are modified by repairing corresponding geometric information.(4)On the premise the all data is valid,the algorithm of automatically constructing a closed solid form the geometric set of discrete faces is explored.Topological relationships between semantic features are built by Boolean operations on the themantic objects.The feasibility of algorithm is verified by the experimental data of CityGML using LOD1 to LOD4 data sets from the official website of OGC.Finally,the topological relationships of semantic features,which are not explicitly stored in the instance document of LOD1,are stores through the TopoADE.This experiment of LOD1 indicates the rationality of extended topological framework.(5)Taking the IFC data as experimental data,we try to build the topology automatically in the domain of Building Information Model.Based on the topological relationships,we propose a dimensionally reduced approach for searching an enclosed room,which is not defined as a building element in IFC standard.Besides,the topological connected network within a floor can be generated according to topological relationships between the wall and opening elements,such as door and window.The tests provide the basis for building-related spatial query and analysis.