3D GIS是GIS的发展方向,其研究尚处于基础理论阶段,目前,市场上还不存在成熟的真3D GIS。2D、3D结合是实现3D GIS的一条有效途径。服务式2D、3D结合GIS则是在服务式构架下实现2D GIS与三维可视化技术的无缝结合,即由GIS服务器提供传统的2D GIS服务,客户端提供用户界面及2D、3D数据融合渲染等功能。实现服务式2D、3D结合GIS的核心是如何在网络条件下,进行大规模数据传输及客户端2D、3D数据的实时融合渲染。本文针对此核心问题提出了基于C/S框架的2D、3D结合GIS系统构架,其核心包括基于LOD(Level of Detail)模型的客户端渲染构架及基于双缓存机制的数据服务构架。本文基于此系统构架开发了一个原型系统,使用ArcGIS Engine开发了GIS服务端,在World Wind开源软件的基础上,实现了三维客户端。二维GIS服务端为三维客户端提供基本的GIS服务,如查询,缓存区分析等。系统运行结果表明该服务式构架解决了服务式2D、3D结合GIS的关键问题,为进一步构建应用系统奠定了基础。该系统构架亦适用于B/S构架。实践证明在此框架的基础上通过将客户端封装为Web控件可实现基于B/S构架的服务式2D、3D结合。

3D GIS will be the next generation of geographic information system (GIS). Ideally, 3D GIS should be developed based on good theoretical foundation. Currently, many researches have been carried out both by academic groups and commercial sector to develop 3D GIS application. So far, there is no ideal 3D GIS product available on market partly due to the complicated topology of spatial objects in 3D environment, inappropriate spatial data structures and hardware limitation. Studies carried out indicated that the integration of 3D visualization technology with current 2D GIS applications could be an alternative for realizing 3D GIS. One obvious benefit of such combination is that it can take advantages of both technologies. Service-based integration aims to realize the integration of 2D GIS with 3D virtualization technology based on service framework. Data transmission speed between remote server and client is the main bottleneck of providing textures for 3D rendering engine. Thus, the key problem of this type of integration is how to maintain the frame rate of rendering in 3D client under the limited data transmission speed. This paper promotes a system architecture based on C/S framework, in which the core is consisted of a LOD-based rendering architecture and a data service architecture based on double cache mechanism, which will help overcome above problems. The double cache mechanism is designed to improve the performance of data serving at both client side and sever side by using a client data cache and a sever data cache. The prototype GIS sever is developed by ArcGIS Engine to provide data and traditional 2D GIS service, for example, spatial querying, for 3D client. The client application is developed with help of World Wind, an open source software, which acts as a user interface. The results obtained by this prototype system show that how this framework helps to overcome the key problem of the integration of 2D service GIS with 3D visualization technology, which would be extended for various applications in feature. This framework is also suitable for B/S framework simply by encapsulating 3D client into a web component.