Research On Urban 3D Data Organization Method Based On Geo-entity

With the rapid development of mapping and modeling technology,a variety of 3D model data has been formed.These 3D model data describe the geometry,texture and semantics of spatial objects in more and more detail.At present,many experts and scholars at home and abroad have done a lot of research on the unified organization method of 3D model,and have made some phased achievements.In the past,different data organization methods were selected according to different data types,which could not meet the needs of different applications.City is an important settlement of human life,which is more prominent in the face of complex and dense urban space.In 3DGIS,when 3D model data depict the complex real world,the same geoentity corresponds to the data expression of multi-source data at different detail levels.How to realize the unified organization of multi-source urban 3D data needs further research.Geo-entity refers to the independent natural or artificial feature with spatial location and common attributes in the real world.According to Geo-entity Spatial Data Specification,the spatial data of geo-entity are divided into large,medium and small scale geo-entity,but it is difficult to satisfy the organization of urban 3D data.CityGML is a general data model for expressing 3D city templates.All models in CityGML can be divided into five different coherent levels of detail(LOD).As the level of detail increases,more details about geometry and themes can be obtained.However,for a variety of reasons,the actual data manufacturer is difficult to produce data in full accordance with the level of detail required by standards such as CityGML.For example,oblique photography model is the surface of the continuous model,there is no single semantic information,and the data accuracy can reach centimeter level,can satisfy some LOD level in terms of geometry specification,but in terms of semantics,but can't meet the specifications of corresponding LOD level,will lead to oblique photography model accurately into CityGML defined LOD level.In this paper,a method of organizing urban 3D data based on unique geographic entity coding and scale division is proposed.The main contents of the paper are as follows:(1)Unique coding of geo-entity—the correlation basis of urban 3D data.The 3D model data is rich and diverse,and the production units and technical means of each model data are different,resulting in the lack of correlation between model objects.Establishing the relation between the model objects is the basis of organizing the urban 3D data uniformly.Geo-entity,as a uniquely identifiable natural or artificial object,is intrinsically related to the model object produced by various technical means,and can be used as the correlation basis of each model object.The unique coding scheme of geo-entity is designed for unique identification of geoentity.Firstly,the benchmark geographical grid model of the coverage area is constructed.Secondly,the unique coding of geo-entity is established by taking the minimum grid as the spatial unit and referring to relevant specifications.(2)Scale grading standards of geo-entity.The geospatial data obtained by any means cannot fully describe the geographical objects,which can only describe part of the features,but the degree of detail varies.Therefore,multi-source heterogeneous 3D data can be regarded as the expression of different scales of geo-entity.For 3D model data in geometry,and semantic differences such as appearance,level of detail of CityGML model,this paper proposes a classification standard of the scale of the geo-entity oriented,based on the model characteristics to differentiate LOD0-LOD4 detail scale,a total of five level of multi-source heterogeneous city unified organization of the urban 3D data to geo-entity.(3)According to the organizational method designed in this paper and the actual project requirements,the prototype system of urban 3D data application management is designed and implemented.The urban 3D data organization method based on geo-entity designed in this paper is applied to the actual project to verify the feasibility of this method.