Component Technology In The Web Gis Development

With the rapid development of Internet, the Web GIS combined by GIS and Internet technology has become the important direction of GIS development at the present time. At the same time, it has become the most effective way of GIS' socialization and popularization particularly as the increasing of user' demands that is using Internet technology to express information on Web and providing user browsing.In 1993 Microsoft first published the COM technology that brought the completely mode for the exploiting of Web GIS. Specialy the appearance of new technology in ATL- DCOM makes it possible in developing the mature and efficient products of Web GIS.PowerlnterMap is a Web GIS product that is come up in a background of this technology. It combines the newest COM > ASP and other correlative technology and uses the oriented-object software integrated way and provides the correlative serves as Web Map browsing> inquiry and analysis for vast numbers of Internet users according to the stable and efficient principle.1 % The design and reality of clientBecause of the limit of Internet's wide , the client must be little enough.Base on this, We use ATL to develop client (ATL control that we performed is about 70KB).Then we take ATL control into ASP page. Using the specific property that IE supports ActiveX technology, We directly send the HTML code and ATL control to client .At client, We realize the display^ zoom out > zoom in> wandering > simple analysis and searching.2% The design and implement of group servers'dynamic load balanceWith the rapid increasiy of Internet .It has become unpredictable for us that the number of visitors. So the servers must have the ability of dealing with the mass and parallel visiting. This mainly depends on the group servers' dynamic load balance. DCOM offers a series of technology for the group servers' dynamic load balance. Though DCOM does not directly perform , it make group servers' dynamic load balance become easy. Base on DCOM, we have designed the mode of group servers' dynamic load balance, we can perform it with transparent manner.ATL and DCOM are the newest development of COM, It's difficult for us to master this two new technology and apply it into practicality. In this paper, we gives some experience in developing process to everybody and hopes to give beneficial reference to the persons who are workong on the development of Web GIS.