The Design And Implementation Of Complex Linear Symbol Base

Map Symbol Base is one of the essential and basic modules of Digital Mapping System and Geographic Information System, while the organization and description of linear symbol is the important and difficult part of map symbol base. Epecially the realization of complex linear symbol has a lot of problems, e.g., some linear symbol can not be selected and modified when the problems happened in the corner of linear symbol; the inefficiency of linear symbol drawing; the symbol base is dependent on specific platform and can not be easily shared, etc. Aimed to solve these problems, after analyzing the structural characteristics of complex linear symbol, the basic unit of linear symbol is summarized with the Object-Oriented thoughts and the description parameters of basic unit has been designed, in addition, rendering algorithm has been designed and optimized in this thesis. The main contribution of this thesis is summarized as follows:1) After analyzing the basic component of linear symbol, three basic line type, i.e., dash line, point line, and solid line has been concluded to describe the linear symbol. The point line is composed by point element, basic component of point element has been analyzed and two basic primitive of point element:polyline and arc has been designed. The parametric description method of line symbol, its basic line type and basic element has been designed.2) Algorithm of linear symbol’s three basic line type has been designed, verified by experiment, the above algorithm is efficient and has less problems in the corner.3) Linear Symbol Base is divided to four modules:the I/O module the conversion module, the rendering module and the design module, which are independent and interdependent. According to such design, the mitigate of system platform running can fully expand the function of linear symbol without effect the structure of the platform system.4) According to the difficulty in designing linear symbol, a symbol designer has been produced, which makes design linear symbol in a parametric what you see is what you get way becomes possible.