现代大地测量参考框架进行精确的卫星定位导航大学毕业论文外文文献翻译及原文

应用大地测量学英文English:Geodesy is a branch of Earth sciences that deals with the measurement and representation of the Earth's geometric shape, gravitational field, and orientation in space. It encompasses various techniques and methodologies for accurately determining the size and shape of the Earth, including terrestrial and satellite-based measurements. Applications of geodesy are widespread and diverse, ranging from mapping and cartography to navigation, land surveying, and satellite positioning systems like GPS. In mapping and cartography, geodesy provides the foundation for creating accurate maps and charts, essential for urban planning, resource management, and environmental monitoring. Geodesy also plays a crucial role in navigation systems, ensuring precise positioning and guidance for vehicles, ships, and aircraft. Land surveying relies on geodetic principles to establish property boundaries, infrastructure development, and construction projects. Additionally, geodesy is fundamental in the operation of satellite positioning systems like GPS, enabling real-time positioning and navigation services worldwide. By accurately measuring the Earth's shape andgravitational field, geodesy contributes to our understanding of phenomena such as sea level rise, crustal deformation, and tectonic plate movement, vital for mitigating natural hazards and managing resources effectively.中文翻译:大地测量学是地球科学的一个分支，涉及地球几何形状、重力场和在空间中的定位的测量和表示。

如何理解大地测量坐标参考框架大地测量是一种用来测量和描述地球表面形状和大小的科学方法。

在大地测量中，坐标参考框架被用来确定地点和地物的三维位置。

这个框架提供了一种标准的方式来描述地球表面上的任何地点，使得测量结果能够被准确地记录和比较。

1. 什么是大地测量坐标参考框架？大地测量坐标参考框架是一种用来描述地球表面上点的位置的系统。

它基于一个共同的基准点和坐标系统，通过测量和计算的方式来确定地球上其他点的位置。

这个框架可以被用来描述地球上的任何地点，无论是陆地、海洋还是空中。

在大地测量中，坐标参考框架通常由水平和垂直两个方向组成。

水平方向上的坐标参考框架被称为大地水准面，它描述了地球表面上点的经度和纬度。

垂直方向上的坐标参考框架被称为大地垂直面，它描述了地球表面上点的高度。

2. 大地测量坐标参考框架的作用大地测量坐标参考框架在地理信息系统、土地测量、工程测量等领域有着重要的应用。

它提供了一种通用的方式来描述地球上的地点，并为测量结果提供了一个统一的参照系统，使得不同测量结果可以进行比较和分析。

在地理信息系统中，大地测量坐标参考框架被用来存储和管理地理数据。

通过将地理数据与坐标参考框架相关联，可以实现数据的空间查询和分析。

这种方式使得地理信息在地图制作、城市规划、资源管理等领域发挥着重要的作用。

在土地测量和工程测量中，大地测量坐标参考框架被用来确定地点的位置和高度。

土地测量帮助测量和划定土地的边界，工程测量则用于测量建筑物、道路、桥梁等工程项目的位置和高度。

通过使用大地测量坐标参考框架，可以实现测量结果的准确记录和分析。

3. 大地测量坐标参考框架的确定确定大地测量坐标参考框架通常需要进行大地测量和数据处理。

在大地测量中，通过使用全球定位系统（GPS）等技术来测量和记录地球表面上点的位置和高度。

采集到的测量数据经过处理和分析，得到经度、纬度和高度的数值。

然后，这些数值可以与国际标准的大地测量坐标参考框架进行比较和转换。

GPS中英文参考文献参考文献：[1] 刘基余.GPS卫星导航定位原理与方法.北京：科学出版社，2003[2] 刘基余，李征航.全球定位系统原理及其应用.北京：测绘出版社，1993[3] 王惠南，GPS导航原理与应用.北京：科学出版社，2003[4] 贾金玲.微型计算机原理与接口技术课程设计指导.重庆：重庆大学出版社，2001.12[5] 潘永雄.新编单片机原理与应用.西安：西安电子科技大学出版社，2003[6] 张鹏.单片机原理及应用.成都：电子科技大学出版社，2004.8[7] 白雪，徐雷钧，刘围海，黄振跃．基于单片机的GPS定位信息采集系统[J]．微计算机信息，2008，24(8—1)：228—229．[8]黄凌．基于单片机的GPS信息处理系统[J]．现代电了技术，2007，(21)：60一61．[9]赵建玲．51系列单片机开发宗典[M]．北京：电了工业出版社，2007．[10]刘一杰，施一民，过静君．全球定位系统(GPS)的原理与数据处理[M]．上海：同济大学出版社，1996．[11]Encyclop?dia Britannica 2007 Ultimate Reference Suite.Version.2007.01.00.000000000 Encyclop?dia Britannica, Inc.2007.01 [8] GS1100 Seriers Operational manual.Verison1.0.Serf Company.2004.11[12] MAX220-MAX249+5V供电、多通道RS-232驱动器/接收器.Rev15. Maxim Integrated Products, Inc.2006.01[13] NMEA Protocol Specification . Verison1.31. Fastrax Oy.2003.06。

Unit14 Datums, Coordinates and Conversions（已知坐标转换）A datum is the mathematical model of the Earth we use to calculate the coordinates and elevations on any map , chart, or survey system . Geodetic datum s define the size and shape of the Earth and the origin and orientation of the coordinate systems used to map the Earth . Hundreds of different datum s have been used to frame position descriptions since the first estimates of the Earth’s size were made by Aristotle . But all coordinates reference some particular set of numbers for the size and shape of the Earth . For example, the Global Positioning System (GPS) is based on the World Geodetic System 1984 (WGS-84) . Many countries use their own datums when they make their maps and surveys—what we call local datums .（基准是我们用来计算任何地图、海图或测量系统的坐标和海拔的地球的数学模型。

外文翻译---GPS的精密单点定位技术在空中三角测量的应用附录1：英文原文ISPRS Journal of Photogrammetry and Remote Sensing YUAN Xiu-xiao(袁绣萧)FU Jan-hong(福剑虹)SUN Hong-xing( 孙红星)The application of GPS precise point positioning technology in aerial triangulationAbstractIn traditional GPS-supported aero triangulation, differential GPS (DGPS) positioning technology is used to determine the 3-dimensional coordinates of the perspective centers at exposure time with an accuracy of centimeter to decimeter level. This method can significantly reduce the number of ground control points (GCPs).However, the establishment of GPS reference stations for DGPS positioning is not only labor-intensive and costly, but also increases the implementation difficulty of aerial photography. This paper proposes aerial triangulation supported with GPS precise point positioning (PPP) as a way to avoid the use of the GPS reference stations and simplify the work of aerial photography. Firstly, we present the algorithm for GPS PPP in aerial triangulation applications. Secondly, the error law of the coordinate of perspective centers determined using GPS PPP is analyzed. Thirdly, based on GPS PPP and aerial triangulation software self-developed by the authors, four sets of actual aerial images taken from surveying and mapping projects, different in both terrain and photographic scale, are given as experimental models. The four sets of actual data were taken over a flat region at a scale of 1:2500, a mountainous region at a scale of 1:3000, a high mountainous region at a scale of 1:32000 and an upland region at a scale of 1:60000 respectively. In these experiments, the GPS PPP results were compared with results obtained throughDGPS positioning and traditional bundle block adjustment. In this way, the empirical positioning accuracy of GPS PPP in aerial triangulation can be estimated. Finally, the results of bundle block adjustment with airborne GPS controls from GPS PPP are analyzed in detail.The empirical results show that GPS PPP applied in aerial triangulation has a systematic error of half-meter level and a stochastic error within a few decimeters. However, if a suitable adjustment solution is adopted, the systematic error can be eliminated in GPS-supported bundle block adjustment. When four full GCPs are emplaced in the corners of the adjustment block, then the systematic error is compensated using a set of independent unknown parameters for each strip, the final result of the bundle block adjustment with airborne GPS controls from PPP is the same as that of bundle block adjustment with airborne GPS controls from DGPS. Although the accuracy of the former is a little lower than that of traditional bundle block adjustment with dense GCPs, it can still satisfy the accuracy requirement of photogrammetric point determination for topographic mapping at many scales.' 2009 International Society for Photogrammetry and Remote Sensing,Inc. (ISPRS). Published byElsevier B.V. All rights reserved.Key words: deformation monitoring; landslide; single epoch GPS positioning; ambiguity resolutionIntroductionAerial triangulation (AT) is the basicmethod for analyzing aerial images in order to calculate the 3-dimensional coordinates of object points and the exterior orientation elements of images. Up until now, bundle block adjustment has been commonly employed for AT, and numerous ground control points (GCPs) are necessary for the adjustment computation (Wang, 1990). In the 1950s, photogrammetrists began exploiting other auxiliary data to reduce the number of GCPs. However, investigation did not achieve an implementing result because of themany technological limitations at that time (Li and Shan, 1989). In the1970s, with the application of Global Positioning System (GPS), the situation changed a lot. GPS can provide 3-dimensional coordinates of surveying points with centimeter accuracy in differential mode, it was therefore applied in AT to measure the spatial position coordinates of the projection centers (referred to as GPS camera stations or airborne GPS control points). In this way, the number of GCPs could be significantly reduced. Block adjustment of combined photogrammetric observations and GPS-determined positions of perspective centers is regarded as GPS-supported AT. Since the beginning of the 1980s, many papers have presented the significant research and experimental results of GPS-supported AT (Ackermann, 1984; Friess, 1986; Lucas, 1987). After about 20 years of these efforts, GPS-supported AT was extensively applied in aerial triangulation at many scales and in all types of terrain. It is particularly beneficial in areas where they are difficult to establish ground control (Ackermann, 1994).In the late 1990s, with the development of sensor technology, an integrated systemof GPS / Inertial Navigation System(POS)was first used in AT to obtain the position and attitude information of aerial images directly. This technology, in theory, can eliminate the need for GCPs. However, research indicates that the digital orthophoto map can be made directly by image orientation parameters obtained via a POS (Cannon and Sun, 1996; Cramer et al., 2000; Heipke et al., 2001), but there will be larger vertical parallax when stereo models are reconstructed using these image orientation parameters and the height accuracy cannot satisfy the requirement of large scale topographic mapping. Therefore, a bundle block adjustment should be made, combined image orientation parameters obtained via the POS and photogrammetric observations (Greening et al., 2000).Whether exploiting GPS data or POS data in AT, DGPS positioning is necessary to provide the GPS camera stations at present. In the DGPS mode, one or more GPS reference stations should be emplaced on the ground and observed synchronously and continuously together with the airborne GPS receiver duringthe entire flight mission. Additionally, signals from GPS satellites should be received as few transmission interruptions as possible. Initialization surveying is also required before aircraft takes off and static surveying should be performed after landing. In the processing of GPS observations, carrier phase differential technique is used to eliminate or reduce GPS positioning errors, including satellite clock error, satellite orbit error, atmospheric delay error, and so on. Generally speaking, it is difficult to emplace proper GPS reference stations when the aerial photographic region is with large scope or difficult to access and communicate. In order to guarantee the quality of aerial images, a survey area must be photographed for a long period, which is result from the shortage of weather suitable for photography. GPS reference stations must therefore remain in place for a long time. Moreover, the accuracy of DGPS positioning is relevant to the length of baseline. The longer the baseline, the weaker the correlation between ionospheric refraction error and tropospheric delay error. Due to the need for spatial correlation of atmospheric delay errors, the lengths ofGPS differential baselines are typically limited to within 20 km if centimeter level accuracy is required with high reliability (Sun, 2004). When it comes to aerial photogrammetry, this is difficult because the length of survey areas is typically more than 200 km and the distance between the survey area and the airport may be greater. For baselines with long length, the atmospheric delay mainly composed of ionospheric delay and tropospheric delay will degrade positioning accuracy significantly. In such cases, even the ionospheric delay can be almost removed by using dual frequency GPS receivers. However, there can still be a tropospheric delay within a few decimeters, meaning that for long baselines, the positioning accuracy is typically in the level of decimeters. At the same time, the establishment of GPS reference stations sometimes makes the implementation of a survey plan difficult due to traffic, communication and cost considerations. As a result, the method of replacing GPS reference stations by Continuous Operating Reference Stations (CORS) was proposed and obtained an accuracy in decimeter level compared with the results obtained by GPS reference stations(Bruton et al., 2001;Mostafa and Hutton, 2001). There are, however, no CORS in most of the survey areas, so this method cannot be applied extensively. With the development of GPS technology, the number of CORS is increasing all over the world and their distribution is more and more reasonable. International GNSS Service (IGS) can provide precise satellite orbit and clock error products with accuracies of 5 cm and 0.1 ns (3 cm). Utilizing IGS products, if the atmospheric delay error can be removed, modeled or estimated at the centimeter level, it will be possible to obtain centimeter level positioning accuracy with only the observation of a single GPS receiver. Zumberge et al. presented a GPS precise point positioning (PPP) method based on an un-differenced mode and achieved centimeter level accuracy for static positioning (Zumberge et al., 1997, 1998). Later, Muellerchoen et al. presented a method for realizing GPS global precise real time kinematic positioning by using single epoch un-differenced dual frequency observations after initialization (Muellerchoen et al., 2000). In this way, centimeter to decimeter level accuracy can be achieved for aerial GPS kinematic positioning at present (Gao and Chen, 2004; Zhang et al., 2006).If GPS PPP technology is applied in GPS-supported AT, only one GPS receiver is mounted on the aircraft and GPS reference stations on the ground are no longer required. GPS-supported AT can therefore be implemented very easily andwith great flexibility, which is obviously significant in large survey blocks or areas with difficult terrain. Therefore, GPS PPP technology is discussed in this paper based on the highly dynamic characteristic of aerial remote sensing. The error law of GPS camera stations obtained by this method is analyzed, and the positioning accuracy and the feasibility of GPS-supported AT using GPS PPP technology are discussed. The goal of this work is to eliminate the need for the GPS reference stations in GPS-supported aerial photography by the GPS PPP technology. This technology can not only reduce the cost of aerial photography but also increase the flexibility of aerial photographic operations,which is beneficial to thewidespread use of GPS-supported AT.2. GPS precise point positioning for aerial triangulation In contrast to DGPSpositioning technology, GPS PPP is a type of absolute GPS positioning which uses IGS precise orbit parameters and clock error products. The main algorithms and correction models for the GPS PPP have been discussed in many papers (Han et al., 2001; Kouba and Heroux, 2001; Holfmann et al., 2003; Chen et al., 2004) and the most widely used data type is un-differenced ionosphere-free carrier phase measurements, or an ionosphere- free combination with carrier phase and code pseudorange measurements. An alternative data type used by some studies is code-phase ionosphere-free combination that aims at accelerating the convergence speed for parameter solutions (Gao and Chen, 2004). In this paper, the single difference model is employed for reasons that will be discussed below. For simplification, error corrections including relativity, satellite phase center offset, satellite wind up, earth body tide, ocean load correction and so on, will not be discussed here. The original un-differenced data type is formed by an ionosphere-free combination of dual frequency GPS data (Kouba and Heroux, 2001):(A-1)Here, j denotes satellite; Q j is the ionosphere-free combination ofL1 and L2 code pseudorange; j is the geocentric distance from the GPS receiver to the satellite j; dt is the GPS receiver clock error; dt j is the clock error of the satellite j, which can be obtained from IGS products; c is the vacuum speed of light; T is the zenith tropospheric delay; Mj is the mapping function of tropospheric delay for satellite j, for which several models can be used; j is the ionosphere-free combination of L1 and L2 carrier phase; Nj is the non-integer ambiguity of ionosphere-free carrier phase combination; "Q and "are the noises. There are five unknown parameters in Eq. (1), including the 3-dimensional spatial coordinates of the receiver (X; Y; Z) lying in j , the zenith tropospheric delay T and the receiver clock error dt. Furthermore, in Eq. (2), besides the same parameters in Eq. (1), the ambiguity Nj is unknown. For these unknown parameters, the ambiguity Nj is constant if the cycle slip is repaired and thezenith tropospheric delay T changes very slowly or remains unchanged over a short time span, for example, over two hours. The receiver clock error dt changes very quickly and the coordinates of the receiver (X; Y; Z) are dependent on the vehicle movement status. In aerial photogrammetric applications, the craft often carries out large maneuvers, the sequential filter based on the dynamic models of all parameters (Kouba and Heroux, 2001) can not be implemented for high accurate positioning because the process noises of the vehicle movement and the receiver clock error are very large. In this case, the recursive least squares algorithm can be used to separate the receiver coordinate and clock error from other parameters which remain constant or change very slowly (Chen et al., 2004). Assuming that X and Y are the two kinds of parameters to be estimated, the observation equation in matrix Form can be written as :(A-2)where L is observation vector; X is correction vector of the coordinates of GPS receiver antenna phase center and clock error; Y is vector of ambiguity parameters and the correction parameters to zenith tropospheric delay; A and B are design matrices; " is the noise vector; 0 is the standard deviation of the noise; P is the weight matrix of observations.附录2：中文翻译GPS的精密单点定位技术在空中三角测量的应用袁绣萧福剑虹孙红星摘要在传统的GPS辅助空中三角测量,差分全球定位系统（DGPS）定位技术用于确定曝光时间透视中心的3维坐标厘米到分米级精度。

现代地理信息技术概论姓名xxx学号xxx学院xxx专业xxx任课老师xxx201x/xx/xx 浅析GPS技术在测绘工程相关领域的应用经过一学期的学习，对“3S”有了一定的认识和了解，个人对GPS 比较感兴趣，同时出于自己来自xxx学院的缘故，在此浅析GPS技术在测绘工程相关领域的应用。

1 GPS 技术概述1.1 GPS 系统构成GPS系统主要由空间部分、地面控制系统、用户设备终端三大部分组成。

GPS的空间部分是由21颗工作卫星和3颗在轨备用卫星组成,以55°的轨道倾角均匀分布在6个距地表20200km的轨道面上。

地面控制系统由监测站、主控制站、地面天线组成。

用户设备部分包括GPS 接收机、数据处理软件及其终端设备3个构件。

如今国内今采用WGS84坐标系统。

1.2 GPS 定位原理GPS定位的基本原理是根据高速运动的卫星瞬间位置作为已知的起算数据,采用空间距离后方交会的方法,来确定待测点的具体位置。

但GPS具体定位的方法原理是不同的,终端操作者可以依据不同的目的使用不同的定位操作方法。

现依据不同分类标准,划分详见表1。

表1 GPS操作方式分类一览表1.3 GPS 技术的特点GPS定位功能包括：（1）可以任意加载各种遥感影像图、传统矢量图、扫描地形图等,并可以自动接边和智能生成缩略图;（2）资源调查属性库自定义、点线面图层定义管理等; （3）高精度面积测量、两点间距离精度测量; （ 4）高精度野外测点与配准;（ 5）多种数据格式转换、各种坐标相互转换、彻底实现了资源调查的无纸化和自动化。

1.4 GPS 测量的特点GPS 测量与以往的测量方式相比，具有自己独特的优势：第一，GPS 测量可以精确测定测站点的三维坐标，可以提供较为准确的数据，其高程精度已经达到四等水准测量的要求了；第二，测量时间短，进行GPS 测量时，动态相对定位仅需几秒钟就可以了，而静态相对定位虽然所需时间多一些，但也最多超不过20min，随着GPS 测量技术的不断完善，软件的不断更新，时间还会进一步缩短；第三，测量精度高。

空间大地测量的应用摘要通过学习空间大地测量学的课程，结合空间大地各项技术的最新成果与进展，系统介绍了目前空间大地测量的各项技术在各领域的应用。

关键字空间大地测量；应用；大地测量技术分类号近年来，随着VLBI技术和卫星导航技术的飞速发展，大地测量学经历了一场划时代的革命性的变革，克服了传统的经典大地测量学的时空局限，进入了以空间大地测量为主的现代大地测量的新阶段。

空间大地测量所求得的点位精度、地球定向参数（极移、日长变化等）的精度、地球重力场模型的精度和分辨率比以前都有了极大的提高。

空间大地测量已经成为建立和维持地球参考框架、测定地球定向参数、研究地壳形变与各种地球动力学现象、监测地质灾害的主要手段之一，并渗透到人类的生产、生活、科研和各种经济活动中，从而使大地测量处于地球科学多种分支学科的交汇边缘，成为推动地球科学发展的前沿学科之一，加强了大地测量学在地球科学中的战略地位。

利用自然天体或人造天体的来精确测定点的位置，确定地球的形状、大小、外部重力场，以及它们随时间的变化状况的一整套理论和方法称为空间大地测量学。

随着空间大地测量成为实现大地测量学科各类目标的主要技术手段, 正主导着学科未来的发展方向和科学地位, 目前正向更高的水平发展。

空间大地测量技术除了卫星重力探测技术(卫星测高、卫星跟踪卫星和卫星重力梯度测量)以外,主要包括全球定位系统(G P S) 、甚长基线干涉测量(VLB I) 和激光测距(L R ) (包括卫星激光测距(S L R )和激光测月技术(L L R ) )。

（一）空间大地测量在卫星重力探测技术方面的应用地球重力场的研究始终是大地测量学科发展最活跃的领域之一。

人类认识地球重力场的水平不仅取决于在全球范围内测定重力和探测重力场信息的技术发展水平, 而且还取决于确定地球重力场的理论发展水平。

目前进行重力探测的方法主要有地面重力测量、卫星重力测量和航空重力测量。

地面重力测量仍然是获取高精度、高分辨率重力数据的手段之一。

卫星定位导航外文翻译文献(文档含中英文对照即英文原文和中文翻译)原文：MODERN GEODETIC REFERENCE FRAMES FOR PRECISE SATELLITE POSITIONING AND NAVIGATIONJ. Kouba and J. PopelarGeodetic Survey Division, Geomatics Canada, Natural Resources Canada (NRCan) 615 Booth Street,Ottawa, Ontario, Canada K1A EO9ABSTRACTThe NAD83 and WGS84 reference coordinate frames were established more than a decade ago to satisfy most mapping, charting, positioning and navigation applications. They are consistent at the 1-2 metre level on a continental and global scales respectively, reflecting the limitations of available data and techniques. With rapid improvementsin positioning accuracy, mainly due to GPS, submetre navigation has become practical and reference frames at the cm to mm level are required by the most demanding users. The IERS Terrestrial Reference Frame (ITRF) was established in 1988 by the International Earth Rotation Service (IERS) to facilitate precise monitoring of the Earth Orientation Parameters (EOP) based on state-of-the-art techniques such as Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR). With the establishment of the International GPS Service for Geodynamics (IGS) in 1994, the ITRF is directly accessible to users world-wide by means of precise global GPS satellite orbit/clock solutions and a large number of IGS monitoring stations. The most recent ITRF solutions, designated ITRF92 and ITRF93, are based on space geodetic observations including GPS up to the end of 1993 providing global consistency at the cm level. The Canadian Active Control System (CACS) facilitates access to ITRF through active participation in IGS and VLBI. Fiducial VLBI points included in NAD83 provide a direct link to ITRF and make it possible to upgrade NAD83 coordinates in order to satisfy positioning and navigation requirements with cm precision in the future. CACS facilitates the most efficient connections to the ITRF and NAD83 reference frames for high precision positioning by GPS as well as for general spatial referencing needs in Canada.1. INTRODUCTIONIn geodesy a reference coordinate frame implies a scale, orientation and coordinate origin as part of a reference system which also includes Earth planetary models and constants necessary for satellite orbit determination, ge- odynamic and geophysical data analysis. Satellite navigation systems made it possible to establish a truly global geocentric reference system which was quickly adapted for precise geodetic positioning, especially over long distances. For the first time it was possible to determine distortions and misorientation of classical geodetic networks around the world. The U.S. Navy Navigation Satellite System (NNSS), also called Transit or simply Doppler (Kershner and Newton, 1962) became the basis for the U.S.Department of Defense World Geodetic System 1972 (WGS72) and later WGS84 which define global geocentric reference frames consistent at about the 1-2 metre level. To upgrade and correct distortions of the classical North American Datum 1927 (NAD27), a readjustment of the geodetic networks in Canada, USA, Mexico and Greenland was jointly undertaken. This new datum, designated NAD83, was nominally made compatible with WGS84 by being geocentric and oriented according to transformed Doppler positions, but in addition the NAD83 adjustment included VLBI (Very Long Baseline Interferometry) baselines. Thus both, WGS84 and NAD83, are consistent at about one metre, mainly due to the limitations of the Doppler techniques (Kouba, 1993). GPS and other space based techniques such as VLBI and Satellite Laser Ranging (SLR) provide data with higher precisions to support studies of crustal dynamics and polar motion which require a more accurate global reference frame. The IERS Terrestrial Reference Frame (ITRF) was established in 1988 and is updated on an annual basis by the International Earth Rotation Service (IERS) to keep it current and to improve knowledge of station velocities which are necessary for maintaining the accuracy of this global reference frame. NAD83 can be related to ITRF precisely for a given epoch by a transformation based on common VLBI stations. The Canadian Active Control System (CACS) provides the most efficient method to upgrade NAD83 coordinates in Canada in order to meet positioning and navigation requirements with cm precision in the future.2. NORTH AMERICAN GEODETIC DATUM: NAD83The North American Datum 1927 (NAD27) was established at the beginning of this century using continental triangulation with a centrally located datum point at Meades Ranch in Kansas, USA (Ross, 1936). Satellite geodesy in the 60's and 70's detected the approximately 100 m offset of the NAD27 origin with respect to the geocenter as well as distortions exceeding tens of meters in some parts of the geodetic control network (Mueller, 1974). A new reference frame wasrequired to facilitate use of efficient and precise satellite geodetic techniques in surveying and navigation. Satellite Doppler positions and several VLBI baselines which had been establishedbefore the end of 1986, were used to provide a framework and to define the geodetic datum in a new way. The North American Datum 1983 (NAD83) was based on Doppler station coordinates transformed to conform with the international convention for geocentric origin, scale and orientation of the reference ellipsoid (NOAA, 1989). Classical geodetic observations for more than 260,000 control points have been readjusted and integrated within the framework to provide the NAD83 coordinates of the horizontal control network monuments for practical use. Thus, NAD83 in its original version provides a reference frame for horizontal positioning with accuracies at the one meter level corresponding to satellite Doppler precision somewhat diluted by errors in the classical triangulation arcs included in the NAD83 network adjustment. At this level of precision there was no need to introduce station velocities and NAD83 is considered to be attached to the North American tectonic plate. The NAD83 reference frame satisfies most practical needs for mapping, charting, navigation and spatial referencing in North America where sub-meter accuracy is not required. However, today the increased precision of geodetic GPS measurements requires a reference frame consistency at a cm level which would facilitate studies of crustal dynamics related to plate tectonics and natural hazards associated with seismic or volcanic activities, etc. The accuracy of the VLBI baselines which contributed to the definition of NAD83 not only provides an effective way to relate NAD83 to more accurate reference frames at a 2cm level (Soler et al., 1992) but also facilitates precision upgrades using accurate geodetic space techniques. Such an approach will assure continuous improvements of positioning accuracy as well as traceability to NAD83 which is of great practical importance.3. WORLD GEODETIC SYSTEM: WGS84WGS84 is a global geodetic reference system which has been established and maintained by the U.S. Department of Defense to facilitate positioning and navigation world wide (DMA, 1991). The terrestrial coordinate reference frame corresponding to WGS84 has been updated to keep pace with increasing precision of GPS positioning andnavigation technology in general use.3.1 ORIGINAL WGS84 TERRESTRIAL EFERENCE FRAMEWGS84 world wide terrestrial reference frame was initially based only on satellite Doppler coordinates transformed in the same way as for NAD83. However, a different set of Doppler stations was used and no VLBI baseline measurements were included in the network adjustment. This approach produced a globally homogeneous geodetic reference frame with an accuracy of 1-2 m reflecting the limitations of the Doppler technique. Station velocities were ignored as they were of little importance. Although the Doppler WGS84 reference frame is comparable with that of NAD83 in North America, the lack of precise VLBI framework makes it impossible to relate WGS84 to current, more accurate reference frames with a precision better than 1m. Significant improvement can be achieved if the WGS84 framework adopted for GPS operations is considered. This WGS84 (GPS) terrestrial reference frame is based on WGS84 coordinates of 10 GPS tracking stations used by the U.S. DoD for generation of operational (broadcast) satellite orbits and clock parameters.3.2 REVISED WGS84(G730) TERRESTRIALREFERENCE FRAMEThe WGS84 (GPS) coordinates of the 10 GPS tracking stations have been revised using several weeks of GPS observations from a global network of 32 stations (10 DoD + 22 IGS) in a simultaneous adjustment of satellite orbits and station coordinates; the coordinates of 8 IGS stations were constrained to the values adopted by the International Earth Rotation Service (IERS) and the IERS value of the geocentric constant of gravitation was used. This improved reference frame for GPS, designated WGS84 (G730) to refer to GPS week 730, shows global consistency at about the 10cm level and uses NUVEL-1 plate motion model for station velocities (Swift, 1994; De Mets at al., 1990). Since the beginning of 1994, DMA has used WGS84 (G730) in post- processing and it is expected to be adopted for the computation of operational (broadcast) GPS satellite orbits in the near future (Malys and Slater, 1994).4. IERS TERRESTRIAL REFERENCE FRAME: ITRFIn order to facilitate precise Earth rotation and polar motion monitoring by modern space geodetic techniques the Bureau International de l'Heure (BIH) established in 1984 the BIH Terrestrial System (BTS84) based mainly on VLBI, SLR and satellite Doppler observations. In 1988 when BIH was superseded by IERS the IERS Terrestrial Reference Frame (ITRF88) was created to meet the following requirements (Boucher, 1990):Figure 1. Residual differences between NAD83 and ITRF92 (1994.0) for the CACSmonitoring stations.(a) it is geocentric with the origin at the center of mass of the whole Earth including the oceans and the atmosphere;(b) its orientation is consistent with the BIH Earth Orientation Parameter (EOP) series for the epoch 1984.0;(c) the station velocity model shall not produce any residual rotation with respect to the Earth crust;(d) the scale corresponds to the local coordinate system of the Earth in the senseof the relativistic theory of gravitation.Since 1988, an ITRF solution has been produced on an annual basis to incorporate new observations and stations as appropriate to satisfy the above requirements. The tectonic plate motion model NUVEL-1 was used to derive station velocities while enforcing the no residual rotation requirement. This combined with the somewhat uneven global distribution of the ITRF stations produced a 0.2 mas/year rotation between ITRF and IERS EOP (IERS Annual Report 1992) which accumulated by 1992 to a significant misalignment of about 1 mas. The NUVEL-1 model station velocities were revised to take into account observed VLBI and SLR station velocities where available, to produce ITRF92 which included about 150 stations. GPS observations offer the most efficient technique for the densification of ITRF when integrated in the VLBI framework which maintains the absolute orientation and scale. Mean station position errors for VLBI and GPS networks included in ITRF92 are summarized in Table 1 which shows cm level consistency for the global solutions (Boucher at al., 1993). Improvements in determination of station velocities and further densification to obtain more homogeneous coverage on all continents will be critical for maintaining and increasing the ITRF accuracy in the future.Table 1. Consistency of VLBI and GPS global solutions included in ITRF92Solution N Weighted RMS [cm] 2D 3DVLBI(GIUB) 7 0.6 0.7 VLBI(GSFC) 70 0.4 0.6 VLBI(JPL) 7 1.1 1.5 VLBI(NOAA) 55 0.3 0.5 VLBI(USNO) 15 0.7 0.7GPS(CODE) 12 0.4 0.7 GPS(CSR) 24 1.2 1.3 GPS(EMR) 17 0.4 0.6 GPS(ESA) 32 3.1 3.4GPS(JPL) 39 0.6 0.7 GPS(SIO) 40 1.3 1.85. TRANSFORMATION BETWEEN TERRESTRIAL REFERENCE FRAMESPractically useful transformations between different terrestrial reference frames are based on their most accurate common set of stations which are then used to determine seven transformation parameters and provide basic RMS information on the consistency of the relationship. Residual systematic differences can be mapped or represented analytically if they exceed significantly the RMS value of the coordinate differences after the transformation. The residual differences between NAD83 and ITRF92 (epoch 1994.0) positions for the Canadian Active Control System (CACS) monitoring stations are shown in Figure 1. However, such deviations should be investigated and corrected if they represent accumulation of systematic errors. Revisions of this kind provide natural upgrade path for any terrestrial reference frame and enhance significantly its practical importance by gradually eliminating unacceptable errors. The WGS84 (G730) reference frame is an example of a comprehensive revision in response to practical needs of GPS applications. Table 2 lists the 7 transformation parameters between the terrestrial reference frames discussed above and ITRF92 (epoch 1988.0). The global consistency of the terrestrial reference frames has improved by almost two orders of magnitude over the last decade as evident from Table 2. It has been achieved by a meticulous application of the complementary techniques of VLBI and satellite geodesy. The maintenance of the cm level terrestrial reference frame consistency requires systematic monitoring of crustal and terrain dynamics including monument stability. Continuous monitoring of the Earth rotational dynamics by VLBI is necessary for high precision applications of satellite positioning and navigation systems which have made this rapid progress in global geodesy possible.Table 2. Transformation parameters with respect to ITRF92(epoch 1988.0)6. ACCESS TO MODERN TERRESTRIALREFERENCE FRAMESThe high precision, global scope and dynamic nature of space techniques, particularly GPS in general use today, demand new approaches to the maintenance and access to terrestrial reference frames. As pointed out above, the modern terrestrial reference frames must be connected to the best available realization of the inertial frame provided by VLBI and must facilitate determination of station velocities in the geocentric coordinate system. This is presently accomplished by a combined solution for a global network of fiducial VLBI stations augmented by SLR and GPS stations for which geocentric coordinates and velocities are obtained from series of observations and geodynamic models; the solution defines a "control network" for a given epoch, e.g. 1988 for ITRF. Monitoring of "control station" velocities and the Earth rotation parameters (ERP), needed for inertial reference, requires continuous observation at some of the "control network stations" which creates an Active Control System (ACS). Such reference system offers two complementary modes of access to its terrestrial reference frame and supports real-time high precision global positioning and navigation.6.1 CANADIAN ACTIVE CONTROL SYSTEMCACSThe Geodetic Survey Division (GSD), Geomatics Canada in collaboration with the Geological Survey of Canada (GSC) has established CACS as an essential component a modern fully integrated spatial reference system to support geodetic positioning, navigation and general purpose spatial referencing. CACS represents the Canadian contribution to the International GPS Service for Geodynamics (IGS) and facilitatesdirect integration of Canadian stations within ITRF. The CACS network configuration (Fig. 1) augmented by about l8 globally distributed IGS stations provides continuous data for daily precise GPS satellite orbit and clock offset determination constrained by about 13 fiducial VLBI stations to facilitate positioning with highest precision for geodetic control networks and crustal dynamic studies as well as generation of high quality orbit predictions forreal-time applications. The quality of the CACS results in comparison to the other IGS Analysis Centers can be seen in Table 3. GSD is also responsible for coordination of the IGS Analysis Centers and combination of their results into the official IGS products (Beutler at al., 1993).Table 3. IGS Combined Orbit Summary, week 0758 (July 17 - July 23, 1994) Mean and standard deviations of transformation parameters. WRMS - orbit RMS weighted by the orbit accuracy codes. Units: meters, mas, ppb, nano-sec, nano-sec/day.Three strategies have been developed for the integration of regional GPS stations and networks in ITRF or related terrestrial reference frames, e.g. NAD83, WGS84. The first strategy uses sequential global processing for addition of data from regional stations to the system of normal equations and obtain updated global solution with coordinates of the regional stations. The second strategy uses the CACS/IGS precise orbits in baseline double-difference processing to establish high precision regional networks for special geodetic and geodynamic applications with mm or ppbprecision (Fig. 2). The third strategy uses the CACS/IGS precise satellite ephemerides and clock offset data and undifferenced GPS observations for single point positioning with accuracy corresponding to the pseudorange measurement precision of the GPS receiver used.DRAO-ALBH Baseline, Length 301.768387 kmSigma=32..95 mmFigure 2. Variations in the DRAO (Penticton) -ALBH (Victoria) baseline length solutions (after Dragert at al., 1994).This rather simple approach can satisfy wide range of spatial referencing and navigation requirements with one meter or better precision (Fig. 3). Real-time wide area differential GPS (WADGPS) service can only be supported by an active control system like CACS which assures continuous, efficient and economical access to the reference frame. In this way all activities and operations can be related to a common, accurate and reliable global spatial reference frame by means of GPS. CACS satisfies both requirements of a modern terrestrial reference frame: maintains a network of fiducial reference stations and provides continuous monitoring and updating of all variable system parameters which are necessary for precise and consistent user positioning.Figure 3. CACS USER POSITIONING INTERFACE: Initial convergence tests based on CACS post-processed orbits/clocks and a single receiver pseudorange/phase ata.6.2 CANADIAN BASE NETWORK - CBNThe traditional method of access to a reference frame is based on differential positioning with respect to control stations with "known" coordinates in the required reference frame. These are determined either during the reference frame definition or the later integration of so called control surveys. Such an approach was necessary due to the elaborate and time consuming procedures used in the past to obtain reference station coordinates with required accuracy. Nevertheless, the need to maintain an accurate terrestrial network of monumented reference stations in addition to an active control system is twofold. Firstly, it provides control points for tecniques other than GPS and facilitates calibration and performance analysis of survey instrumentation and procedures. Secondly, it densifies the network of active control points while providing direct connections to classical geodetic horizontal and vertical control networks. Station spacing is generally greater and special considerations are required for site selection and monumentation to support higher precision and efficiency of operations. The determination of station velocitiesrequires regular reoccupations and systematic analysis of monument stability and crustal dynamics. The Canadian Base Network (Fig. 4) is to play an important role in the integration of the horizontal and vertical geodetic control networks and support studies of crustal deformations and seismic hazards in Canada.Figure 4. Proposed station spacing for the Canadian Base Network (CBN).7. CONCLUSIONSGPS technology offers users the most versatile, accurate and economical system for geodetic positioning, navigation and general purpose spatial referencing to date. In order to maximize system performance and effectiveness, GPS applications depend on continuous monitoring of the GPS satellites with respect to conventional terrestrial and celestial reference frames. Modern terrestrial reference frames are based on the spacetime coordinate system centered at the geocenter and must take account of Earth tectonic plate motion anddeformation to provide a cm level accuracy potential. ITRF has been implemented and maintained to satisfy the highest accuracy positioning requirements on the global scale. NAD83 has been implemented to satisfy mapping, charting and navigation applications where sub-meter accuracy is not required; however the VLBI framework provides an upgrade path to a cm accuracy NAD83 reference frame rigidly connected to the North American plate. The transformation parameters (Table 2) facilitate transformations between the reference frames to accommodate user needs. The active control system (ACS) provides efficient and economical direct access to the terrestrial reference frames with the required accuracy and facilitate real-time high precision spatial referencing and navigation.REFERENCESBeutler,G., J. Kouba, T. Springer, Combining the orbits of the IGS Processing centers, Proc. IGS Analysis Center Workshop, 20-56, 1993.Boucher, C., Definition and Realization of Trrestrial Reference Systems for Monitoring Earth Rotation, in Variations in Earth Rotation, D.D. McCarthy and W.E. Carter (eds), 197-201, 1990.Boucher,C., Z. Altamimi and L. Daniel, ITRF station coordinates, a paper presebted at the IGS Network Operations Workshop, Silver Spring, Md., USA, Oct. 18-21, 1993. DeMets,C., R.G. Gordon, D.F. Argus and S. Stein, Current plate motions, Geophys. J. Int., 101, 425- , 1990.Dragert, H., M.Schmidt and X. Chen, The Continuous GPS Tracking for Deformation Studies in Southwestern British Columbia, ION GPS 94, Salt Lake City, Utah, September 20-23, 1994.DMA TR 8350.2, Department of Defense World Geodetic System 1984, Its Definition and Relationships with Local Geodetic System, 2nd Ed., Sep. 1991.IERS 1992 Annual Report, International Earth Rotation Service (IERS), Observatoire de Paris, July 1993.IERS 1993 Annual Report, International Earth Rotation Service (IERS), Observatoirede Paris, July 1994.Kershner, R.B. and R.R. Newton, The TRANSIT System, J. Inst. Navigation, 15, 129-144, 1962.Kouba, J., A review of geodetic and geodynamic satellite Doppler positioning, Review of Space Physics, 21(1), 27- 40, 1983.Kouba, J. , P. Tetrault, R. Ferland and F. Lahaye, IGS data processing at the EMR Master Active Control System Centre, Proc. of 1993 IGS Workshop, 123-132, 1993. Malys,S., and J.A. Slater, Maintenance and enhancemens of the WGS84, ION GPS, Salt Lake City, Utah, September 20-23, 1994.McCarthy, D.D., IERS Standards (1992), IERS Technical Note 13, Observatoire de Paris, July 1992. Mueller, I.I., Review of problems associated with conventional geodetic datums, The Canadian Surveyor, Vol.28, No.5, 514-523, December, 1974.NOAA Professional Paper NOS 2, North American Datum of 1983, Edited by C.R. Schwarz, National Geodetic Survey, NOS, NOAA, U.S. Department of Commerce, 1989.Ross, J.E.R., Triangualtion in Ontario and Quebec, Geodetic Survey of Canada Publication No. 90, Department on Interior, Ottawa, Canada, 1936.Soler, T., J.D. Love, L.W. Hall, R. H. Foote, GPS results from statewide High Precision Networks in the United States, Proc. Int. Geod. Symp. on Satell. Positioning 6th, 573-582, 1992.Swift, E., Improved WGS84 Coordinates for the Defense Mapping Agency and Air Force GPS Tracking Sites, ION GPS 94, Salt Lake City, Utah, September 20-23, 1994.现代大地测量参考框架进行精确的卫星定位导航J.库巴和J. Popelar大地测量部，测绘加拿大，加拿大自然资源部（NRCan）615展位街，渥太华，安大略省，加拿大K1A EO9在NAD83和WGS84坐标参考框架建立超过十年前，以满足大多数测绘，制图，定位和导航应用。

附录一：英文原文A GIS WEB –APPLICATION FOR POWER SYSTEM OF CRETEJ。

Syllignakis，C。

Adamakis, T.M。

PapazoglouThe Technological Educational Institute of Crete （TEIC)，Greece ABSTRACTGeographical Information System （GIS）applications are very helpful tools for displaying and analyzing informationfor several technological fields. The research group of Electrical Power System Lab (EPSL) of TEIC is developing aGIS software application for displaying the operational conditions of the power system of Crete，presenting alsocritical information and statistical data for system’s characteristics。

This tool is intended to help training of engineersin the Electrical Department of TEIC to simulate and visualize power system operation and characteristics。

Besides,this tool is very helpful for a power system engineer in observing the whole system operations and system's data。