关于GIS缓冲区的建立问题

Problem of Buffer Zone Construction in GIS

在对多种方法编程实践的基础上，本文对绘制平行曲线特别是形成缓冲区的两种主要方法（角分线法与圆弧法）进行了分析对比。角分线法带来很多异常情况，连同其补充校正措施，该方法就失去其相对简易性。相反，圆弧法是在强化判断（凸凹判断和弦弧可控逼近）的基础上，最大限度地确保双线的等宽性。文中提出二重数学模型：形成双线的几何算法模型和针对自相交问题的关系处理模型。除了重点对单一目标进行研讨外，文末对具有集合特征的树结构和网结构的缓冲区建立问题也进行了原则性讨论。

On the basis of program practice concerning several approaches to construct buffer zone for cartographic and GIS data handling. Analysis and comparison between method of angular bisectrix and method of circular arc are analyzed. The former often brings out graphic anomalies which can require further multi criteria judgement and corresponding correction processing. That would make this method difficult to be used.As the opposite with the method of angular bisectrix a circular arc method for construction of double parallel lines of buffer boundary has been developed. The latter method is based on the enhanced judgements (convex/concave judgement, controllable chord to arc approximation) guaranteeing the width equality to the utmost extent. The core issue is the treatment of circular arc method which is based on the double mathematical models: the geometric model for constructing the double parallel lines and the relation handling model for detecting the islands and overlapping areas. Both islands and overlapping areas have symmetric structure properties: islands of left bound line appears in anticlockwise,but overlapping areas clockwise. For right boundary line the situation is completely opposite. The island polygons should serve as components of final parallel lines or buffer boundaries. At last, scheme of construction buffer zones for tree structure of line objects and complex network configuration is proposed.