The Importance of Time Synchronization in the Local Networks of the Science and Application Center for Lunar and Deep-space Exploration

The data acquisition stations and the data processing center of the Science and Application Center for Lunar and Deep-space Exploration (SACLuDE) are located at different geographical sites. They respectively have their own local networks and interconnect with each other through access to the core data network. This paper describes the clock drift in the computer and other networked devices building up the infrastructure of the above local networks. The network time variance of the stochastic model is also estimated. The poor precision of network synchronization will bring about potential hazards to the network operation and application running in the networks, which is clarified in the present paper. At the end of the paper, a cost-effective and feasible solution is proposed based on the Global Position System (GPS) and the Network Time Protocol (NTP).     

关于省局域网远程访问的探讨

随着人们对信息技术“灵活性”的要求,远程访问技术广为应用,为了外出工作人员的工作便利和节约经费,远程访问技术在山西省地震局的实施也迫在眉睫.在远程同步、安全维护和设备软件的管理等问题上,结合山西省地震局的实际情况,探讨了使用点对点协议PPP,远程访问服务器RAS,拨号安全服务器与调制解调器组合,拨号连接实现远程访问功能,防火墙、网关保护、病毒软件及网管软件等维护数据安全的可能性.     

基于XML的多级异构空间数据库的同步架构

分析了多级异构空间数据库同步的关键问题和难点，提出了一种基于XML的多级异构空间数据的同步架构，该架构在“全国国土资源数据交换中心试点建设项目”中得到成功应用。     

GPS接收机动态检定场中的时间同步问题

首先,阐述了时间同步问题在GPS接收机动态检测中的重要性.其次,就相机快门延迟检测原理、检测方法进行了详细的讨论,检测出所使用的相机快门时间延迟约为90 ms,但有时会出现突变,得出了仅仅依靠机械快门无法实现相机在动态条件下的同步拍摄的结论.然后,结合液晶快门的控制对相机时间同步等问题进行了讨论.最后,给出了数码相机配合液晶快门以实现相机高精度同步的方法.     

《北京市规划信息发布系统》的特点与研制方法

建立了规划信息发布系统的运行环境,加工整理、入库和发布了100多个GB的空间数据和多媒体数据,系统具有查询浏览、系统管理等功能,同时具有多窗口空间数据联动,方便的角色管理,灵活高效的海量数据发布等特点。系统的运行实现了规划信息共享,提高规划设计人员工作效率的预期目标。     

BOOK REVIEWS

Book Reviewed in this article: Rabat: Urban Apartheid in Morocco . Janet Abu -Lughod . Marketplaces in a Developing Country: The Case of Western Nigeria . Isaac Ayinde Adalemo . Farming Development and Space: A World Agricultural Geography . Bernd Andreae . Section and Party: A Political Geography of American Presidential Elections, from Andrew Jackson to Ronald Reagan . J. Clark Archer and Peter J. Taylor . Women and Space: Ground Rules and Social Maps . Shirley Ardener , ed. European Progress in Spatial Analysis . R. J. Bennett , ed. The Origins of Academic Geography in the United States . Brian W. Blouet Geographic Perspectives on Global Problems . Ronald Reed Boyce . Seasonal Dimensions to Rural Poverty . Robert Chambers , Richard Longhurst and Arnold Pacey eds. The New Nationalism and the Use of Common Spaces: Issues in Marine Pollution and the Exploitation of Antarctica . Jonathan I. Charney , ed. Communications Tomorrow: The Coming of the Information Society . Edward Cornish , ed. The Design of Suburbia . Arthur Edwards . Explorer on the Northern Plains: Lieutenant Gouverneur K. Warren's Preliminary Report of Explorations in Nebraska and Dakota in the Years 1855–56–57. With an Introduction by Frank N. Schubert . The Changing Climate: Responses of the Natural Flora and Fauna . Michael J. Ford . Essentials of Physical Geography . Robert E. Gabler , Robert J. Sager , Sheila Brazier , and Daniel L. Wise. The Road to Jaramillo . William Glen . Valued Environments . John R. Gold and Jacquelin Burgess , eds. Proximity and Preference: Problems in the Multidimensional Analysis of Large Data Sets . Reginald G. Golledge and John N. Rayner , eds. A Search for Common Ground . Peter Gould and Gunnar Olsson , eds. Geography: Its History and Concepts . Arild Holt -Jensen . A Population Geography . Huw R. Jones . The Human Mosaic: A Thematic Introduction to Cultural Geography, 3rd ed. Terry G. Jordan and Lester Rowntree . Urban Social Geography: An Introduction . Paul Knox . The Anatomy of Job Loss: The How, Why and Where of Employment Decline . Doreen Massey and Richard Meegan . The Information Society as Post-Industial Society . Yoneji Masuda . Map Librarianship, 2nd ed. Harold Nichols . India: Cultural Patterns and Processes . Allen G. Noble and Ashok K. Dutt , eds. The God that Limps: Science and Technology in the Eighties . Colin Norman . Geography: An Introductory Perspective . Robert E. Norris , Keith D. Harries and John D. Vitek . The Politics of Technology Assessment . David M. O'Brien and Donald A. Marchand . Ethnic Segregation in Cities . Ceri Peach , Vaughan Robinson and Susan Smith , eds. Churches and Church Membership in the United States, 1980 . Bernard Quinn , Herman Anderson , Martin Bradley , Paul Goetting and Peggy Shriver . Energy in Australia: Politics and Economics . Hugh Saddler . Development from Above or Below? The Dialectics of Regional Planning in Developing Countries . Walter B. Stóuhr and D. R. Fraser Taylor , eds. Human Impact on the Ecosystem . Joy Tivy and Greg O'Hare . Plants and People: Vegetation Change in North America . Thomas R. Vale . The Mapmakers: The Story of the Great Pioneers in Cartography from Antiquity to the Space Age . John Noble Wilford .     

基于Geodatabase的数据复制技术研究

G IS的飞速发展对数据分发和管理提出了新的要求,即野外用户的离线编辑、多级应用、分布式维护、故障恢复以及多项目数据管理等等。基于Geodatabase的数据复制技术为解决这些问题提供了可能。通过版本、复本(Rep lica)、同步、协调等几个关键技术,深入地研究了Geodatabase复制技术,为基于ArcG IS项目数据的分发、拷贝和分布式管理提供了解决方案和思路。     

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基于Geodatabase的数据复制技术研究

GIS的飞速发展对数据分发和管理提出了新的要求,即野外用户的离线编辑、多级应用、分布式维护、故障恢复以及多项目数据管理等等.基于Geodatabase的数据复制技术为解决这些问题提供了可能.通过版本、复本(Replica)、同步、协调等几个关键技术,深入地研究了Geodatabase复制技术,为基于ArcGIS项目数据的分发、拷贝和分布式管理提供了解决方案和思路.     

统计同步算法原理及在局域网中的应用

针对局域网中计算机间的时间同步问题,分析了统计同步算法PCS的基本原理,介绍了局域网中网络延迟精确测定的方法,提出了利用一台时统设备实现局域网中PCS算法精度测试的方法,给出了频率漂移的修正公式,并在局域网中对算法性能进行了测试.测试结果表明,计算机时钟的漂移是影响算法精度的主要因素.经过频漂修正,PCS算法性能得到了很大的改善,同步周期较设计周期大大增加,算法同步精度在20min内优于1 ms.