网格GIS体系结构及其实现技术

网格 GIS是实现广域网络环境中空间信息共享和协同服务的分布式 GIS软件平台和技术体系。将地理上分布、系统异构的各种计算机、空间数据服务器、大型检索存储系统、地理信息系统、虚拟现实系统等 ,通过高速互连网络连接并集成起来 ,形成对用户透明的虚拟的空间信息资源的超级处理环境就是网格地理信息系统。本文在分析网络空间数据特征的基础上 ,提出了网格 GIS的 5层体系结构模型,分析了空间(元)数据标准、空间服务标准、分布空间对象技术、构件与构件库技术、基于框架的互操作技术、中间件技术等 ,它们是实现该系统的关键技术。

Architecture of Grid GIS and Its Implementation Techniques

Grid geographical information system (Grid GIS) is a hardware infrastructure and distributed software platform to share information and service collaboratively for wide-area spatial information distributed processing. On the internet, computational, storage, and network resources are heterogeneous and reside in different security domains. This makes the spatial data processing grid environment much more challenging than traditional distributed computing environments, which typically consist of homogeneous machines under the control of a distributed operating system. Grid GIS is the virtual super-computing environment for spatial data handling which connects computers, spatial databases, huge data store system, other GIS, virtual reality systems,and so on in the heterogeneous application environment to one system (Grid GIS). In this paper, we discuss the basic spatial services that must be provided by a grid GIS infrastructure to enable high-performance applications to be distributed over the wide area. We survey recent technical papers on grids and spatial data processing and focus particularly on the key implementation techniques for GRID GIS,such as, spatial data(metadata) standard, spatial data service standard, distributed spatial object, component and component database, spatial data interoperability and middleware, from the Globus project and SIG project. We also propose the 5 tiers model, which consists of client application, service converting bridge, function server,spatial data engine and database server, for architecture of Grid GIS on the basis of analysis the feature of spatial data in the network. Our solution for data sharing and service cooperatively is to decompose the name space (metadata) into a top layer which is under centralized control, and at the lowest level, where the resources themselves reside and the need for complex relationships is greater. The communication at the top level is GXML. For instance, a portal may request information from a GIS server. It would issue a query in a language like XPath (step 1). The XPath query would be sent to the SQL database server (2), which converts it to an SQL query, executes the query (3) and returns the result as a GXML document (4). Transformation to the document may be necessary (5) before returning the document to the portal.