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Generating online map for Skudai using the Minnesota Map Server
3. The Minnesota Map Server
The Minnesota Map Server was originally developed as free map server software containing various freeware systems such as Shapelib, FreeType, Proj.4, libTIFF and etc. It runs under Windows and UNIX operating systems and supports various formats both raster and vector datasets. In general, it relies on the CGI mode program, Map file and Template file. Parts of the following text are based on available online resources. 3.1 The CGI mode program The CGI mode program of Minnesota Map Server is called Mapserv. The current version of Mapserv program is 3.6.3. It is a component to store all freeware systems. According to Richard W. (2003), the Map Server executable is called directly from CGI mode, and renders the entire HTML page based on parameters passed in the query string, and static configuration files stored on the web server. 3.2 The Map file The Map file is presented as ASCII file. It configures basic information for Minnesota Map Server mechanism such as map’s unit, projection and the path of the data. Besides, it is used for object definition. Every mechanism is considered as object in Map file like map object, label object, layer object, projection object, legend object, class object and so forth. Each object comprises several parameters. Nevertheless, it is not necessary to include every object in Map file. Only the required object needs to be defined. 3.3 The Template file For rendering image on user's web browser, the Template file is required. Basically, the Template file is an HTML file with specially tagged replaceable parameters designated with square brackets (Richard, 2002). When the map server received queries from users, it reads the Template file and generates map objects to reply to the users. The parameters in the square brackets would be replaced by the exact path of the output file. 3.4 The client- server architecture  Figure 1. System Architecture of web based GIS. Figure 1 shows the overview of client-server architecture. It consists of the client side and server side. In general, the whole architecture is divided into three domains, namely, first tier, second tier and third tier. The first tier comprises users and the web browsers that are located at the client side. The second tier is related to the web processing which contains the web server, user interface and map server. Finally, the third tier is the database tier containing spatial and attributes data. Apparently, the Minnesota Map Server is located in the second tier. In order to access to the Skudai online map, users need web browser like Internet Explore, Netscape Communicator or Opera. With the correct Universal Resources Locator (URL), users can access to the web site of Skudai online map. Indeed, the web server will search the related web site according to the URL. However, before displaying the interface, the Minnesota map server will retrieve the spatial data from the database. A complete interface of the Skudai online map includes spatial data display. |