动线法自动制图的关键算法设计与实现

动线法(即运动符号法),能综合表达空间实体或现象的作用方向、运动路线、数量增减、质量变化等,是计算机地图制图的重要方法之一。本文分析了直线动线符号在信息表达中存在的局限性,以及曲线动线符号所具有的优势,对曲线动线符号的组织形式、位置、颜色、方向、宽度、曲率等方面作了分析,同时对曲线动线符号提出了制图算法,具体包括:曲线符号模型算法、避障路径算法、汇流与分流算法等;并以MapServer开源软件作为平台,利用C++语言进行程序设计,建立了Web的动线法自动制图算法实验系统,且以河南省流动人口数据为例,进行算法应用分析。结果表明:该算法极利于时空数据的可视化表达,具有很好的应用前景。

Study of the Cartographic Algorithm on Flow Line Symbol

The flow line method occupies a very important position in cartography. It is able to synthetically ex- press the direction of actions, the movement routes, the increase or decrease of the number, and the quality change of spatial entities or phenomena. Flow line method is a difficult subject in computer graphics, which has not been satisfactorily resolved. The traditional fixed-line method is linear symbols. However, there are many limitations in the practical application of linear symbols. To solve this problem, the author proposed the correla- tion algorithm of curve line symbol and developed a WEB-side system for the moving line method with respect to adaptive cartography, which is based on the open source software MapServer. This article is mainly consisted of three parts： the flow line symbolic algorithm, the database management system, and the map display system. The flow line symbolic algorithm was discussed based on the map display system developed by the Visual Stu- dio 2010 platform, which was consisted of curve symbolic algorithm, obstacles avoiding algorithm, and conflu- ence and difference algorithm. The database management system was established based on the shape file format of spatial data and Oracle environment attribute data. The map display system was used for WEB-side adaptive map display and other interactive functions. In the article, the floating population data was used as an example to verify and describe the system functions of the thematic map display, the hazard avoidance, and the confluence and difference calculations. According to the thematic map, we could analyze the floating population data easily, accurately, and intuitively. This provides great assistances in data supporting and decision making for other stud- ies of floating population and related disciplines. In addition to the floating population, the system is also adapt- ed to the data presentation and analysis of economic development, social factors, military combat, natural phe- nomena, and so on. It can accomplish the functions including curve symbol drawing, obstacle avoidance, and confluence and difference calculations. That is, the flow line symbol algorithm is a great help for the visualiza- tion of temporal expression data, and it has broad application prospects.