图层级矢量地图裁剪计算模式与算法策略

Clipping Computing Model for Vector Map at the Layers' Level

矢量地图裁剪是商业GIS软件平台重要的基础功能之一。而各种商业GIS平台的矢量地图裁剪效率存在较大差异,其中,ArcGIS效率较高。本文提出了一种矢量地图裁剪计算模式:首先,筛选与裁剪要素外接矩形框(MBR)相交或者包含于该矩形框内的被裁剪要素;然后,对筛选出的被裁剪要素构造四叉树索引,根据被裁剪要素的类型采用不同的计算模式完成裁剪;最后,采用线程池技术实现并行高效的裁剪计算过程。实验结果表明,本文提出的方法在矢量地图裁剪方面与ArcGIS 10平台的效率相当。

Clipping function is one of the fundamental functions in Geographic Information System.The efficiency of clipping function can greatly affect the overall performance of data processing in GIS application,especially when clipping large vector data.This paper proposes a new clipping computing model to effectively fulfill the clipping function for different types of clipped layers according to their different attribute and geometry characteristic,such as point,line,polygon,multi-point,multi-line,multi-polygon and so on.This clipping computing model consists of the following three steps： first of all,using clip-layer’s Minimum Bounding Rectangle to select features from clipped-layer,where the features must intersect with or within the clip-layer’s Minimum Bounding Rectangle;secondly,using Feature ID to build revised quad-tree index for the clip-layer features;lastly,using thread-pool to fulfill clip computing in parallel.A performance test was carried out using four different vector data layers.The result shows that the performance of clipping function based on this clipping computing model is as efficient as the one fulfilled in ESRI’s ArcGIS 10.0.CPU-intensive is one drawback of the implementation of this model at its current form.