对WebGIS在网上传输的矢量空间数据进行压缩的方法进行了研究,并在文献[1]提出的矢量空间数据压缩方法的基础上,在以下4个方面有了新的发展(1)对地图坐标数据不仅可以用int型,甚至可以用short型代替传统的double型或float型;(2)得到数据映射范围的计算公式;(3)可用映射范围为虚拟屏幕,对矢量地图上弧段的型值点进行"滤点压缩".如果"锯齿"的台阶宽度stepWidth＝1,图形的精度是无损的;如果stepWidth>1,精度有损;(4)用"长边加点"来处理"偏移量压缩"中,弧段两相邻型值点间x或y的偏移量大于127的个别"长边".在进行了一系列的压缩措施后,可以使矢量地图的数据量压缩率达80%以上.

This paper introduces author's work in compress to vector spatial data, which will be transported in Internet/Intranet. On the basis of vector spatial data compression method, which is proposed by[1], the authors proposes next four innovation:(1)For vector spatial data, not only integer but also short data can be used to replace traditional double or float data. (2)The map data are mapped to a“virtual screen”, the formula of“virtual screen”width is: width=DispWidthPixel×MaxEnlargeRatio/stepWidth①. (3) In the mapping process, execute “filter points compression”to pattern points of arc(including polygon' s boundary arc and line' s arc). In the formula①, if stepWidth=1,“filter compression”has no loss in precise of map displayed, else stepWidth>1, it has precise loss in map displayed. (4)“Long edge adding point”to deal with exception of“Offset compress”to pattern points in arc, which offset in adjacent two points may larger than 127. After these compressions, a map vector data may be compressed to 20% or less.