共查询到20条相似文献，搜索用时 578 毫秒
1.
Virtual differential GPS based on SBAS signal 总被引：2，自引：0，他引：2
In order to access the satellite-based augmentation system (SBAS) service, the end user needs access to the corresponding geostationary earth orbit (GEO) satellites that broadcast the augmentation information for the region. This is normally not a problem for aviation and maritime applications, because an open sky is typically available for such applications. However, it is difficult to access the GEO satellites directly at high latitudes for land applications because of the low elevation angles to the GEO satellites (e.g., 4–22° in Finland to the European geostationary navigation overlay services [EGNOS] GEO satellites). Results from a driving test of 6,100 km in Finland show that the EGNOS GEO satellites can be accessed in only 51.8% of the driving routes. Furthermore, it is also difficult to access the GEO satellites from city canyons, because the high buildings block the GEO signals. This article presents a solution to solve this problem by creating virtual differential GPS (DGPS) reference stations using the SBAS signal in space (SIS). The basic concept is to convert the SBAS signal to Radio Technical Commission for Maritime Services (RTCM) signals, and broadcast the converted RTCM signals over the wireless Internet using the Internet radio technology. Therefore, access to the SBAS service will not be limited by low elevation angles to the GEO satellites because the converted RTCM data streams are disseminated over the wireless Internet. Furthermore, the SBAS service can then be accessed via a legacy DGPS receiver. Two test cases have been carried out with the prototype system developed by the Finnish Geodetic Institute. The test results showed that the positioning accuracy of the virtual DGPS solution was about 1–2 m at 95%, which was similar to that of the standard WAAS/EGNOS solution. The positioning accuracy was not degraded, compared to that of the standard wide area augmentation system–European geostationary navigation overlay services (WAAS/EGNOS) solution, as long as the distance between the rover receiver and the virtual DGPS reference station was less than 150 km. A preliminary driving test of 400 km carried out in southern Finland showed that the availability of the virtual DGPS solutions was 98.6% along the driving route. 相似文献
2.
张群;张雯;李飞雪;李满春;陈东 《东北测绘》2013,(4):13-16
WebGIS优势是通过互联网对地理空间数据进行发布和应用,以实现空间数据的共享和相互操作。将WebGIS和富客户端技术引入Web服务器日志管理领域,从总体设计、数据库设计、实现框架等几个方面设计了Web服务器日志管理系统开发框架,并开发了某工业园区信息共享平台日志管理系统。该系统可以高效便捷地实现网络访问数据空间可视化、访问流量在线监控、访问数据统计与分析等功能,为Web服务器运行维护提供科学的决策依据。 相似文献
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Sea ice data has significant scientific value for climate, environmental impact and engineering studies leading to the construction of facilities in Arctic waters, as well as to support tourism and fishing planning. Large collections of such data are acquired, compiled, produced and maintained by national and international agencies such as the Canadian Ice Service (CIS). Some of these data collections have been made available online. However, current Internet‐based sea ice data dissemination practices do not foster easy access to and use of the data, especially given the amount of the archived sea ice data and the nature of their spatial changes and high temporal variations. This article reports a research effort in developing a web‐based geographical information system (GIS) that facilitates the access and use of the historical sea ice data. The system provides online access, exploration, visualization, and analysis of the archived data, mostly in the form of ice charts, within a web‐based GIS. The results from a prototype development indicate that web GIS, developed using Rich Internet Application (RIA) technologies, provides added values in serving sea ice data and suggests that such a system can better accommodate more advanced sea ice data access and analysis tools. 相似文献
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研究在已实现可视通信的ISDN多媒体卡上，通过芯片的功能复用，设计一个驱动程序模型，以实现ISDN多媒体卡的拨号上网功能。简要介绍了ISDN接入因特网的通信协议体系，详细探讨了ISDND信道的呼叫过程，分析了拨号上网原理有如何与Widnows系统的远程访问服务结构相结合。给出了一个基于NDIS标准的ISDN多媒体卡的小端口驱动程序的设计与实现方案。 相似文献
7.
Hu Shao 《International Journal of Digital Earth》2019,12(3):250-269
For geospatial cyberinfrastructure-enabled web services, the ability of rapidly transmitting and sharing spatial data over the Internet plays a critical role to meet the demands of real-time change detection, response and decision-making. Especially for vector datasets which serve as irreplaceable and concrete material in data-driven geospatial applications, their rich geometry and property information facilitates the development of interactive, efficient and intelligent data analysis and visualization applications. However, the big-data issues of vector datasets have hindered their wide adoption in web services. In this research, we propose a comprehensive optimization strategy to enhance the performance of vector data transmitting and processing. This strategy combines: (1) pre- and on-the-fly generalization, which automatically determines proper simplification level through the introduction of appropriate distance tolerance speed up simplification efficiency; (2) a progressive attribute transmission method to reduce data size and, therefore, the service response time; (3) compressed data transmission and dynamic adoption of a compression method to maximize the service efficiency under different computing and network environments. A cyberinfrastructure web portal was developed for implementing the proposed technologies. After applying our optimization strategies, substantial performance enhancement is achieved. We expect this work to facilitate real-time spatial feature sharing, visual analytics and decision-making. 相似文献
8.
Julia Wagemann Oliver Clements Ramiro Marco Figuera Angelo Pio Rossi Simone Mantovani 《International Journal of Digital Earth》2018,11(1):7-25
ABSTRACTBig Earth Data has experienced a considerable increase in volume in recent years due to improved sensing technologies and improvement of numerical-weather prediction models. The traditional geospatial data analysis workflow hinders the use of large volumes of geospatial data due to limited disc space and computing capacity. Geospatial web service technologies bring new opportunities to access large volumes of Big Earth Data via the Internet and to process them at server-side. Four practical examples are presented from the marine, climate, planetary and earth observation science communities to show how the standard interface Web Coverage Service and its processing extension can be integrated into the traditional geospatial data workflow. Web service technologies offer a time- and cost-effective way to access multi-dimensional data in a user-tailored format and allow for rapid application development or time-series extraction. Data transport is minimised and enhanced processing capabilities are offered. More research is required to investigate web service implementations in an operational mode and large data centres have to become more progressive towards the adoption of geo-data standard interfaces. At the same time, data users have to become aware of the advantages of web services and be trained how to benefit from them most. 相似文献
9.
none 《The Cartographic journal》2013,50(1):61-72
AbstractSome, but not all, branches of the tourist industry make heavy use of maps. The industry has discovered the marketing potential of the Internet but in many cases has not yet fully exploited the extra potential of web maps compared to the traditional paper maps. Web maps can up-to-date tourist information very well but they have to be carefully designed to take account of the limitations of the medium. To be most effective, web maps should be basically simple and convey sufficient information interactively, on request. The map and symbol design should convey intuitively where and how this interaction can take place. This paper summarizes the typical faults found in tourist web map design and provides suggestions on good design practice. 相似文献
10.
《制图学和地理信息科学》2013,40(3):153-165
With the progress of mobile GIS technology there is a great potential for adopting wireless communications and Internet mapping services for regional environmental management programs and natural habitat conservation. This paper provides an overview of a NASA-funded research project that focuses on the development of mobile GIS tools and wireless Internet Map Server (IMS) services to facilitate environmental monitoring and management tasks. By developing and testing wireless web-based map/image servers, mobile GIS applications, and global positional systems (GPS), this research created an integrated software/hardware infrastructure for a prototype mobile GIS application. The mobile GIS prototype allows multiple resource managers and park rangers to access large-size, remotely sensed images and GIS layers from a portable web server mounted in a vehicle. Users can conduct real-time spatial data updates and/or submit changes back to the web server over the wireless local area network (WLAN). This paper discusses in general the major components of mobile GIS, their current technological limitations, and potential problems during implementation. Key research agenda for mobile GIS are identified with suggestions for future research and development. 相似文献
11.
Recent developments in data visualization, developer Application Program Interfaces (APIs), and web services reinforce a long American tradition of statistical mapping and innovation at the US Census Bureau. Consistent with other international statistical agencies, the Census Bureau has used contemporary innovations in statistical mapping and data visualization to disseminate national census results for over 14 decades. The US Census Bureau’s data products and analyses have enabled decision makers and the public to access census results quickly and easily. The new information technology environment requires the Census Bureau to more rapidly expedite these results and deliver mapping products to new customers as well as to its traditional data consumers. The Census API has empowered developers and commercial companies to test the limits of a new emerging world of big data solutions. This article presents some of the most recent data visualization products from the Census Bureau, including an expanding Data Visualization Gallery to merge geospatial information and statistics on the map. 相似文献
12.
面向多种网络带宽环境的远程教学视频传输技术研究 总被引：1，自引：0，他引：1
龚自康 《武汉大学学报(信息科学版)》2006,31(4):368-371
面向网络教育教学视频传输的需求，对视频传输所涉及的视频编码、网络带宽自适应等一些关键技术进行了研究。 相似文献
13.
The EGNOS service will provide better positioning availability and accuracy than that from the standalone GPS solutions. However,
in order to access the EGNOS service, the end user needs to access the corresponding GEO satellites that broadcast the augmentation
information for the region. This is not a problem normally for aviation and maritime applications because an open sky is always
available for such applications. However, an open sky is not always available for land applications because of the obstacles
in the vicinity of the end users, for example, in the city canyons. The situation gets worse for the regions at high latitudes
because the elevation angles to the GEO satellites are rather low (e.g. 4–22° in Finland). This article describes briefly
the SISNeT technology, designed and developed by the European Space Agency, which allows accessing the EGNOS SIS via the Internet.
It will describe in detail the handheld SISNeT receiver, designed and developed by the Finnish Geodetic Institute under ESA
contract. The SISNeT data server is an IP-based server that acquires the EGNOS messages from an EGNOS receiver, and broadcasts
them over the Internet in real-time. The handheld receiver consists of a GPS PC-card receiver, a GPRS (or GSM) card phone,
and a pocket PC as the host platform. The receiver software is a Windows CE-based package with a multi-process and multi-thread
architecture. It simultaneously receives: (1) the EGNOS SIS over a GPRS wireless connection and the Internet and (2) the NMEA
messages from a serial connection to a GPS receiver. It decompresses and decodes the EGNOS messages, and utilizes the information
in the messages to estimate the EGNOS-corrected coordinates, which are finally delivered to the end user via a virtual COM
port. The virtual COM port has been implemented as a stream interface driver in the Pocket PC. It can be accessed in the same
way as the physical COM port in a GPS receiver is accessed. Therefore, it is easy to interface to any third-party applications.
The test results show that the handheld SISNeT receiver can provide a positioning accuracy of about 1–2 m for the horizontal
components, and 2–3 m for the vertical component in real time. Due to the poor performance of the wireless connection, 10–30%
of the EGNOS messages can be lost depending on the services provided by the wireless network operators. The impact of the
messages lost on the positioning accuracy is about 0.5 m in both the horizontal and vertical components.
Electronic Publication 相似文献
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网络地图制图中的主要问题及其解决方案 总被引：10，自引：5，他引：5
本文介绍了网络地图制图的概念和分类,探讨了当前网络地图制图面临的主要问题,包括网络地图信息发布的结构模式、网络地图设计需要考虑的因素以及缩放的非自适应性等,根据国内外相关的研究及GML与SVG技术的最新进展给出了初步的解决方案。 相似文献
16.
互联网的发展要求提供个性化的网络地图自动制图服务。文中运用Web Servers和专家知识库耦合技术研究面向需求的启发式网络地图自动制图原理和方法,该方法将不同用户的网络地图需求视为对地理空间信息一系列的启发式再识别过程,提取出相应的需求参数建立用户兴趣模型,并运用相关算法实现数据的加载以及对地理实体的符号化表示。实践表明,该系统实例可以改善互联网上面向用户需求的个性化网络地图自动制图服务。 相似文献
17.
智能时代泛在测绘的再思考 总被引：2，自引：0，他引：2
本文首先给出泛在测绘的定义和内涵,然后将传统测绘与泛在测绘进行了比较分析,指出由于互联网实现了人与人的信息便捷交互,互联网时代的泛在测绘最显著的推动力就是为满足人与社会及人与环境的多种需求,人本身也成为了测绘的对象。同时,对环境变化的动态感知,对人与环境关系的感知、认知和相应服务成了泛在测绘的重点特色要素。本文还指出互联网因其位置的虚拟性和网络时间标准过低,无法满足对物理世界协同感知和远程广域协同管控的需求,因此互联网、物联网必须向具有精准时空位置感知能力的泛在网演进。文章论述了“泛在网”随着互联网和物联网的演进,是具有“无时不有,无所不在”时空特性的感知网络,并且随着需求的扩展,正演进出“无所不包,无所不能”的智能化需求态势。目前,只有包括北斗在内的全球卫星导航系统,即GNSS技术,能够赋予泛在网在广域和全球范围内具有时空位置感知和管控的能力。在泛在网的支持下,泛在测绘正在发展以实时精准时空感控为特征,以实现陆海天空网一体化、室内外一体化,并实现人与物理世界及虚拟网络世界交互的感知、探测、认知和调控。由此,泛在网也成为智能时代的关键信息基础设施。为了理解智能时代泛在测绘的需求,文章从自然智能及时空位置观出发,对于智能、智慧和人工智能的定义做了新的梳理。针对智能时代人工智能中跨界融合、人机协同、群智开放和自主操控4个热点研究方向及其在军事、工程、实时高精地图及地震预警等的应用,论述了泛在测绘在其中所发挥的基础性、关键性和协同性作用。本文最后还展望了网络虚拟世界的泛在测绘、数字孪生虚拟人的构建及国家安全“制时空权”等智能时代泛在测绘的新领域发展趋势。 相似文献
18.
电子地图的发布与共享可通过网络出版平台实现,以物联网为基础的电子地图网络出版模型能够实现从客户终端、数据信息传输到网络出版商服务端一体化的网路出版模式。提出了一种基于物联网共享空间的电子地图网络出版模型体系。首先构建了物联网共享空间模型,提出搭建电子地图网络出版模型的需求和思路。以感知层、网络层和应用层3层基本结构为底层模型构建了客户终端模块、数据传输模块和数据处理模块,并以集合论的概念定义了不同模块存储数据信息的数据库,在此基础上搭建了物联网电子地图网络出版体系。最后通过模拟实验和测试验证了模型系统的可行性。 相似文献
19.
R. G. V. Baker 《Journal of Geographical Systems》2005,7(3-4):361-379
The Internet has been publicly portrayed as a new technological horizon yielding instantaneous interaction to a point where
geography no longer matters. This research aims to dispel this impression by applying a dynamic form of trip modelling to
investigate pings in a global computer network compiled by the Stanford Linear Accelerator Centre (SLAC) from 1998 to 2004.
Internet flows have been predicted to have the same mathematical operators as trips to a supermarket, since they are both
periodic and constrained by a distance metric. Both actual and virtual trips are part of a spectrum of origin–destination
pairs in the time–space convergence of trip time-lines. Internet interaction is very near to the convergence of these time-lines
(at a very small time scale in milliseconds, but with interactions over thousands of kilometres). There is a lag effect and
this is formalised by the derivation of Gaussian and gravity inequalities between the time taken (Δt) and the partitioning of distance (Δx). This inequality seems to be robust for a regression of Δt to Δx in the SLAC data set for each year (1998 to 2004). There is a constant ‘forbidden zone’ in the interaction, underpinned by
the fact that pings do not travel faster than the speed of light. Superimposed upon this zone is the network capacity where
a linear regression of Δt to Δx is a proxy summarising global Internet connectivity for that year. The results suggest that there has been a substantial
improvement in connectivity over the period with R
2 increasing steadily from 0.39 to 0.65 from less Gaussian spreading of the ping latencies. Further, the regression line shifts
towards the inequality boundary from 1998 to 2004, where the increased slope shows a greater proportional rise in local connectivity
over global connectivity. A conclusion is that national geography still does matter in spatial interaction modelling of the
Internet. 相似文献