网络地图渐进式传输中的粒度控制与顺序控制

Granularity and Order Issues in Progressive Transfer of Web Map

网络地图渐进式传输中数据粒度剖分与传输顺序是该过程控制的两个基本问题,数据粒度过于精细,会获得高分辨率的动画效果,但付出的代价是数据量增大;传输顺序则反应了适应不同领域用户需求从重要到次要数据流导出的先后次序。通过空间数据网上传输与其他视频、动画、图像数据传输的对比,提出了空间数据粒度控制的3个层次划分,即要素级、目标级、几何细节级,通过多个实例应用分析讨论了粒度剖分精细与数据量压缩的技术途径。关于传输顺序建立了数据逻辑组织的空间尺度与语义层次组合矩阵,通过数据元素线性扫描的矩阵行、列优先不同顺序,提出空间尺度优先与语义层次优先的传输过程,讨论了两种传输过程的适用范围。

Data granularity and transmission order are two basic questions when transferring steaming maps progressively over web. The map data with high granularity is able to result in high resolution animation but the data volume increases greatly. The transmission order reflects the data stream sequence from coarse to refined at different domains. This study investigates the hierarchical structure of map data organization and presents a granularity classification with three levels, namely feature level, object level and geometric detail level. Through example analysis, the study discusses the application of three granularity partitioning in progressive transmission as well as the strategies to reduce data volume. For transfer order analysis, a mat of semantic and scale is built to describe the map data set and two kinds of transmission order is offered to apply in different progressive transfer processes, namely the semantic priority order and the scale priority order.