Research And Realization Of Spatial Information Grid Service Model For Mobile Devices

The emergence of mobile internet with its personalized mobile communications and massive internet information has changed people's life and working. Mobile computing will become mainstream computing environment, and mobile GIS becomes to the important growth point in GIS domain. Specifically, restricted to its own conditions, mobile devices experience small memory, low capacity, narrow bandwidth and frequent disconnection issues. In the network environment, spatial data is large and complex, the multifarious spatial information services which rely on different platforms and technologies are difficult to communicate and transfer. Therefore, how the massive information and powerful application services extend from internet to mobile devices, and how the spatial information services meet the mobile users' requirement at any time and any place become to the hotspots in GIS research field.The distributed grid resources provide new services and locations to mobile devices. Mobile users can dynamically connect to the grid in anywhere and communicate with other nodes. After analyzed the devices' position information and service requests, the grid resource management system seeks out the most appropriate spatial information service from rich grid resources, then call the service and feed back the result to mobile users, as a result, the consistent services are provided transparently to the numerous mobile users.Combining grid GIS and mobile GIS, a new open spatial information grid service mechanism is discussed based on the analysis of the latest computer technology and GIS research. Focused on mobile devices' low capacity, narrow bandwidth and frequent disconnection characteristics, making full use of mobile GIS, grid computing, web services, embedded development, and other related technologies, the Spatial Information Grid Service Model for Mobile Devices (also named as M-SIG) is put forward and designed. On the basis of M-SIG, the internet description, organization and management mechanism of data and function services, the grid resource management and scheduling, and the service calling method for mobile devices, are discussed in detail. Mainly include the following aspects:Firstly, discusses the technical issues involved in the combination of mobile GIS and grid GIS. Based on the analysis of geographic information services, mobile GIS. grid GIS, and other related technical, the technical issues that involved in the combination of mobile GIS and grid GIS includes: the spatial information services that fully consider the characteristics of mobile devices and fit for the mobile users need to be established; a reasonable mechanism for scheduling grid resources and information fault-tolerant strategy should be researched; the spatial data compression and the wireless network asynchronous data transmission must be supported; the spatial data access mechanisms for the balance of remote data access and local data storage need to be considered; the humanistic man-machine interface should be designed. Secondly, designs the M-SIG model. Based on the analysis of the mobile environment characteristics, a mobile user oriented spatial information grid service model (M-SIG) is designed, and the specific methods are presented. M-SIG is divided into spatial information service layer, grid management layer, wireless transmission layer and mobile terminal layer. The spatial information service layer is consisted by the numbers of mobile spatial information services in the network; the grid management layer supplies a geographic portal to deal with the mobile users' requests and manage the mobile services; the wireless transmission layer is the bridge between mobile user and grid service center; the mobile terminal layer, which access the grid by a lightweight embedded GIS program, is the client of the model.Thirdly, explores the management mechanism of mobile spatial information service resources in grid environment. To decrease the bandwidth consumption, reduce the network latency, and fully considering the network instability, the way that build grid system for managing mobile spatial information services is discussed, and the grid management mechanism is designed and realized. Using the independently developed spatial database engine-MRSSDE, the complete process for constructing a mobile spatial information service is introduced detailed. Then, through the grid directory and agent technology, the distributed heterogeneous mobile spatial information services are managed unified according to certain rules, so the requirement of parallel and implicit service communication in the grid environment is met.Fourthly, studies on the spatial information service calling method for mobile devices in grid environment. The mobile devices use a lightweight embedded GIS program to access grid. First of all, the mobile device captures the GPS signals from GPS receiver, parses and processes the signal to position information; then, the GIS program organizes the XML request and sends to the grid service center; the center transfers the compressed spatial data which obtained by service calling back to the device asynchronously through a wireless network; the GIS program builds cache and cache index on the receive data, and uses the cache elimination mechanism to manage it; finally, the program displays the result on the device screen.Fifthly, develops prototype of the Mobile Spatial Information Grid Service System. By using simulation technologies and GIS components, a prototype of the Mobile Spatial Information Grid Service System is developed based on M-SIG model, and the structure of M-SIG is realized on the whole. Through the system operation and performance testing, the M-SIG model is validated to be reasonable and effective.Research, testing and the prototype examples show that, the design of M-SIG model is effective, reasonable and feasible. The research adds mobile users to grid and explores the key technologies, such as mobile spatial information service mode, grid management mechanism and mobile client method, to solve the series problems brought from the existing mobile device characteristics which including low capacity, narrow bandwidth and frequent disconnection. The problem of how to extend the massive information and powerful application services from internet to mobile devices is solved theoretically and technically, and it provides a practical solution for efficiently providing diversified spatial information services to the mushroomed mobile users.