Basically, a Browser/Server (B/S) model is adopted in the system design where nearly all computing load is located on the server side, while the client side is only responsible for displaying. In this project, SOA is used to facilitate data communication and interactive operations for the reason that each web service is an independent unit in SOA. The general structure of the web-based UMS using SOA is described as follows (Figure 2). In Figure 2, the server side is composed of GIS web service providers, an image cache server, a web server and a firewall.
Figure 2. Structure of web-based UMS using SOA
In response to the two basic types of urban data at the City of Windsor, two GIS web service providers are devised, respectively a vector data service provider and an aerial photo service. Web service providers are computer servers to publish maps. The vector data service provider is an Object-Relational Database (ORD) based server where all GIS vector data is stored and indexed. The aerial photo service provider is a RDMS based server. High resolution aerial photos are stored in RDMS as pyramid images that can accelerate data distribution at different scales. ArcSDE, a middleware that can facilitate data management, data transfer, and data interaction in one RDMS or among RDMSs, is used to help the data communication between the database servers and map servers.
In order to enhance the efficiency, an image cache server is placed in this system. Maps are usually static, but most map servers render WMS data every time they are queried. This situation can result in unnecessary processing and increased waiting times. In this UMS, an image cache server is added to store all map tiles. When a user requests a map from the cache server, the map server does not have to process the request again, but, instead, responds with a cached image. As a result, computing load on servers can be significantly reduced. Once tiles are stored, the process of map rendering can be speeded up many times for a more seamless user experience.
The web server is used to receive requests from online users and send response back to them. For the network security, a firewall is installed between the image cache server and the web server to prevent internal systems from unauthorized attacks from the internet. One of the greatest advantages of this design is that only an internet browser is required on the client side to display interface and requested responses.
4.1.GIS Web Service
The crucial component in SOA is web service (Reviewed in Section 2.2). Specifically for this project the web service consists of vector data web service and aerial photo web service. The vector data web service provider provides vector data web services and the aerial photo web service provider provides aerial photo web services.
4.2.1Vector Data Web Service
To construct vector data web service provider, PostgreSQL and GeoServer are utilized (Figure 3). Vector data is originally in Shape format....