Designing And Optimizating The Map Symbol Database Based On GDI+

The map symbol database is an very important part in Digital Mapping System and Geographic information system. GDI+ is the new generation graphic-device port in Microsoft. Compared with GDI, It has more powerful function in processing graphic image which can bring a new rendering technology to map symbols.By analysing the characteristic of GDI+, the author summarized the symbol-unit of the symbols using hierarchical methods. Furthermore, the special data structure has been designed to describe symbol-unit. Finally, the map symbol database has been decelopped and several optimized methods with GDI+ have been achieved. The main works are listed as follows:(1) Five kinds of point symbol units, i.e., round, corner, arc, rectangle and equilateral triangle, are summarized according to the feature of point symbols, and give the units special data structure and describe composite structure for each point symbol based on units;(2) The author subdivided linetype to solid line and dotted line, and designed their special data structureis. Then proposed the method to split line symbol and two drawing methods on dotted line.(3) Region symbols split boundary and filled base class, and their special data structure is designed. The boundary can be drawn by the way of line symbol; The filled base class contain color filling,linear filling,GDI+ template filling and point filling. Meanwhile, according to the cut function of GDI+, the method to draw region with or without hole is proposed.(4) C++ structure of annotation is designed. According to the GDI+, note function is initially implemented and providing simply editing function.(5) There is a corner-problem using GDI+ to implement develop complex linear symbols in cartographic symbols for fundamental scale maps, i.e., the marked symbol is not marked uniformly at the junction of line segments. In order to solve the problems, the authors present a method to draw linear symbols based on unit distance, The modified method presented in this paper not only solved the corner-problem, the efficiency of drawing the complex linear symbols also has been improved(6) In order to make up the deficiencies in symbol drawing for GDI+, some schemes are proposed, which contains double cache technology using GDI+ in VC++,the quick-filled algorithm about using point symbol and local refresh technology. It obviously improve the tempo and quality for map symbol database.