Module Design for Map Projection Transformation Based on Object Oriented Methods

Map projection transformation is a key research issue in cartography as well as in GIS. With the continuous updating and improvement of geographical data, effective handling of map projection transformation for geographic information is needed. In this paper, a map projection transformation module developed is presented based on object-oriented methods and discuss the advantages of the methods, with the design and implementation of the module explained in detail. In a VC-6.0 platform, a number of systems have been developed including Cnvt-Coordinate-System, I-Coordinate-System, Geo-Coordinate-System, Prj-Coordinate-System, and Ellipsoid-Set. Among these systems, the Cnvt-Coordinate-System is a key system that draws other relevant methods to accomplish the projection transformation operation. It is concluded that by extending the Geo-Coordinate-System and Prj-Coordinate-System, the module can implement projection transformation between different geographic coordinates systems, or different projection systems, or between the two types of systems. This module can make projection transformation fast and efficient, possesses strong expandability and is easy to maintain.