地球信息科学学报 ›› 2015, Vol. 17 ›› Issue (9): 1029-1038.doi: 10.3724/SP.J.1047.2015.01029

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基于RTP的矢量数据流式传输研究

苗茹1(), 宋佳2,3,*()   

  1. 1. 河南大学计算机与信息工程学院 遥感信息处理实验室,开封 475004
    2. 中国科学院地理科学与资源研究所 资源与环境信息系统国家重点实验室,北京 100101
    3. 江苏省地理信息资源开发与利用协同创新中心, 南京 210023
  • 收稿日期:2015-03-16 修回日期:2015-04-26 出版日期:2015-09-10 发布日期:2015-09-07
  • 通讯作者: 宋佳 E-mail:mr1015@126.com;songj@lreis.ac.cn
  • 作者简介:

    作者简介:苗茹(1979-),女,河南开封人,博士,讲师,研究方向为空间数据处理与可视化。E-mail: mr1015@126.com

  • 基金资助:
    国家自然科学基金青年基金项目“面向地图可视的矢量数据流式渐进传输研究”(41201411);资源与环境信息系统国家重点实验室自主部署项目“陆地表层系统数据-模型共享研究与应用示范”(O88RA900KA)

Streaming Transmission of Vector Data Based on RTP

MIAO Ru1(), SONG Jia2,3,*()   

  1. 1. School of Computer and Information Engineering, Henan University, Kaifeng 475004, China
    2. State Key Lab of Resources and Environmental Information System, Institute of Geographical Sciences and Natural Resources Research, Beijing 100101, China
    3. Jiangsu Center for Collaborative Innovation in Geographic Information Resource Development and Application, Nanjing, 210023, China
  • Received:2015-03-16 Revised:2015-04-26 Online:2015-09-10 Published:2015-09-07
  • Contact: SONG Jia E-mail:mr1015@126.com;songj@lreis.ac.cn
  • About author:

    *The author: SHEN Jingwei, E-mail:jingweigis@163.com

摘要:

针对WebGIS中大规模矢量数据的网络传输问题,提出采用流式传输方式分批次向客户端传输所需数据,从而达到矢量数据在线实时应用的目的。通过研究流式传输机制,建立了适应于矢量数据流式传输的服务框架;按照流式传输的要求,对矢量数据进行分块组织,保证每个批次的要素作为独立的单元传输并在客户端处理;在传输过程中,实时传输协议实现了矢量数据流式传输机制,并参照流媒体文件“边传边播”的模式,设计了矢量数据的封包和解包算法。该方法实现了矢量数据的发送和接收,达到了多次往复传输的目标,且能通过差错控制和压缩加密等手段提高数据传输效率、保证数据传输质量和安全。实验证明,矢量数据的流式传输能降低约一半的数据传输量,有效地提高了传输效率,降低了系统响应时间。

关键词: 网络地理信息, 流式传输, 流媒体协议, 空间要素, RTP数据包

Abstract:

Over the past decade, WebGIS has been widely adopted in various applications to visualize and share geospatial information over the Internet. To address the Internet transmission problems regarding large-volume vector data, streaming transmission based on streaming media transmission protocol is proposed. This paper focuses on the organization mode and the streaming transmission mechanism of vector data, and a service framework for vector data streaming transmission is put forward. The framework consists of server-side vector data preprocessing, streaming progressive transmission, client-side vector data reconstruction and application. A vector data structure is designed which is taken to be an independent group storage. Each group is a separate transmission unit, and the grouped features can be handled immediately after they arrive at the client side. This structure can support the data structure of point, polyline, polygon and other basic geometrics and abide by the OpenGIS standard encoding specification. The server-side preprocessing divides the originally stored vector data into several groups for progressive transfer. Referencing to the multimedia model, we propose an RTP-based streaming transmission schema on the basis of analyzing the packet headers of the RTP and RTCP. The RTP payload format is called vector data stream (VDS), and it is composed of a stream header and a stream body. The combination of RTP method with UDP for streaming transmission has better transmission efficiency than the XML-based WFS for web mapping applications. The error control method and security mechanism we proposed make up UDP's unreliable connection issue. The results are compared with WFS using 1:100 million Chinese basic geographic databases. The comparison reveals that the transfer size of WFS is larger than VDS and the transfer time of streaming transmission is approximately half of WFS's. Thus, the outline of a large-volume vector data map could be viewed quickly based on the proposed mechanisms and algorithms. The experimental results demonstrate the technical feasibility and usability of this approach.

Key words: Web GIS, streaming transmission, streaming media protocol, spatial feature, RTP packet