Spatial Data Model and Visualization for Digital City

With the development of computer technique and Internet,the concept of CyberSpace is formed.But different from our real world,the CyberSpace is structureless and chaotic,with no fixed topology,centers or boundaries.What can change the CyberSpace as our real world is the digital earth and city based on the 3D GIS and virtual reality technique.However,the 3D GIS spatial data model is not mature and difficult to be applied in practice,with less cooperation with the virtual reality.Thus,it is necessany to design a new spatial data model to meet the demand the application and visualization of digital city.In this paper,an Object-oriented 3D spatial data model for digital city is introduced.In this model,the 3D vector spatial data,digital elevation model and digital ground image data are integrated,which will provide more advantage for the visualization of digital city with virtual reality technique.As a new component of Geostar software,the CCGIS software is buidat on this spatial data model,and will be introduced,and how to issue the spatial data issue of a digital city.In Section 1,the lack of current 3D GIS model is pointed out,mainly is the more complex data model and huge data.The Visualization of digital city with VR is too difficult.The photogrammetry and remote sense provide us more digital ground images,This images can give us a overview of the city.With the digital elevation wich can be gained by photogrammetry,we can get the the airscape.This will fit the level of detail concept in the VR field.In Section 2,we introduces the objected-oriented spatial data model,which integrates the vector data,digital ground image and digital elevation model data.Section 3 introduces the CCGIS software,and the detail about how to organized the city's data with the software.Section 4 discusses the application of level of detail in the visualization of the city's scene,and the visnalizativn of the interior of 3D building.In the first filed,the digital ground image is directly looked as the first LOD level; The visualization of DEM which take advantage of digital ground image as texture is looked as the second LOD level.The last LOD level is the geometric data of spatial object,DEM and digital images.In the later field.In the visualization of spatial object,there are two LOD levels.The first is the object's exterior boundary,such as box,and the second level is the detail of object's outline.In more situation,we want to visit the interior of a building,this paper provide a way to solve the problem:we can build many 3D surfaces for the door and windows of the building.each surface will be related two scenes.With the switch related to the entries,different scene will be displayed.At last,the author analyzes the development of digital city in the future,and points out that the cooperation with the distributed GIS,and distributed virtual reality technique is the main goal of the information system.