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Design and Implementation of a COM-based Electronic Map System
Wu Xiaofang Ph.D candidate Her major research interests include cartography COM electronic map system and GIS theory Du Qingyun Cai Zhongliang Xu Zhiyong Laboratory of GIS Ministry of Education Wuhan University Wuhan, 430079 China Introduction Geographic Information System(GIS) is a new technology that begins since the middle of 60’s. By developing for several decades, GIS has been applied to all kinds of fields such as geology, national defense, public security, infrastructure, agriculture and land planning etc, which provides the major functions for the management, analysis, handling and visualization of the geographic data. Therefore, GIS has become one of the important technologies in geography (WU Fa-dong, 2001). The way of traditional GIS software development is to construct the system step by step from the bottom. However, some problems are arising gradually over time. Firstly, the application becomes more and more complicated, which has difficulty in continuously developing and maintaining. At the same time, the tight inner structure of system can make some functions not be deleted, replaced, updated and reused easily. At last, the application lacks for the competence of cooperating with others, and can’t be integrated with other systems easily. With respect to the shortages of traditional method, Component Object Model(COM) technology appears, which is the key to resolve the problem that software development falls behind hardware for a long time(TAN Ren-chun, 2003). In the mode of COM technology, one software system is composed of many objects that cooperate with each other, and each object provides the special functions as the standard and open interfaces in order to communicate with others (LIU Dan, 2002). It is a efficient way to apply COM technology into GIS software development, which gets rid of the repeated development work, promotes the progress of GIS technology, and will bring the great chance to GIS development (HUANG Jian-ye, 2002). Electronic map, as one part of GIS, is a new map category that is derived from the combination of digital technology and traditional cartography. It is one modern information production which takes the visual digital map as the background and uses the multimedia such as text, sound, animation and video to show all kinds of information. (REN Fu, 2001). At present, the successful electronic map software, Atlas 2000, which is developed here in Telecarto studio, can meet the need of users. However, when developing and maintaining Atlas 2000 continuously, we still faces the same problems of traditional GIS software development. Therefore, considering the reuse of knowledge and technology, cross-platform programming, and secondary development easily, a COM-based electronic map system, TeleMap is developed. TeleMap is an ActiveX which is based on the electronic map software, Atlas 2000 and integrates road navigation, map projection, cartographic symbolization by the means of COM technology. Design of Electronic Map COM Electronic map can be displayed on the electronic screen in real-time. As usual, an electronic map system includes many functions such as map visualization, edit, management, analysis, multimedia play and so on. Therefore, when designing a COM of electronic map, many factors need to be considered, for example the source of data, structure of data, management of database, visual style of map, way of playing multimedia etc. Besides, the query function of GIS is considered specially in order to meet the need of all kinds of users. Architecture of Electronic Map COM By analyzing and summarizing the functions of electronic map software, TeleMap is divided into nine components: TeleMapBase, TeleMapSave, GeometryObject2D, TeleMapDisplay, TeleMapSymbol, TeleMapProject, TransportNetwork, VehicleNavigation and TeleMapTransferData. Each component not only realizes its own functions, but also is related with the other components. TeleMap manages these components and is responsible for their mutual communications. They work together to implement the basic functions of electronic map. See Figure 1 for the architecture of TeleMap.  Figure 1 : Architecture of electronic map COM
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