数码城市GIS的设计与实现

The Design and Implementation of CyberCity GIS

在介绍用于数码城市GIS建设的CCGIS体系结构的基础上 ,讨论了不同细节层次的三维建模方法、集成化空间数据库管理方式 ,包括基于面向对象思想的矢量、影像和DEM三库一体化的空间数据库模型和三维动态可视化表示机制等。该系统已被用于上海、深圳和北京等城市的数码小区示范工程建设。实践证明 ,它是建设数码城市的有效平台。

The first section of this paper gives a brief introduction to CyberCity,and then the CCGIS architecture which consists of three parts,the 3D creator and editor,the integrated databases management system and the 3D representation and visualization platform is presented.In the second section,the methods of 3D modeling concerned with LOD are introduced.Especially for efficient 3D data capturing and modeling,based on the object_oriented idea,CCGIS proposed a feature classification and coding scheme,according to which the 3D coded data can be sampled very conveniently using the photogrammetric workstation.On the other hand,a TIN based algorithm can be adopted to create the multiscale 3D city models automatically with high efficiency using these coded data (feature points and lines).The 3D creator and editor can not only create its own 3D city models from the 3D data and/or 2D data plus height attributes,but also import the 3D models created by 3DS or by CAD,and the 3D models also can be edited,for example,to copy,to move,to delete,and to modify any kind of objects in the model. In the next section,the proper 3D data model concerned with the requirements of OpenGL based rendering are presented at first.Then the integration of different databases like the digital elevation models,digital orthoimages and 3D city models is discussed.For CyberCity,since the huge data volume,its proper organization and spatial database index are quite important for data retrieving.The version of 1.0 CCGIS just provides an initial solution for this purpose,which is based on the hybrid system of relational database and file system.But this is not ideal,because the total data access efficiency is dissatisfactory.Moreover,it is very difficult to maintain the convenience and reliability of multiusers' operation and network transmission.So it is necessary to test the integration management of all the data related to the CyberCity using object relational DBMS like Oracle8.16,etc. At last,an interactive visualization platform is introduced,this platform provides the choices of 3D animation or virtual cityscape,and the visual impact can be satisfactory through modulating the various display parameters,such as the rotations around the 3 axes,the field of view and the depth,the mode of walking through or flying over,and the animation route,and so on. The initial version of CCGIS had been used for a few pilot CyberCity projects ,such as ShenZhen,Shanghai and Beijing.The modeling methods and data model adopted in CCGIS are good choices for CyberCity construction.In the near future,next version of CCGIS with more powerful functions will be carried out.