The GPS Toolbox ITRF Transformations

The GPS Toolbox is dedicated to highlighting algorithms and source code utilized by GPS engineers and scientists. If you have an interesting subroutine or program you would like to share with our readers, please pass it along so that we might continue to bring you this column; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here, or to leave a request for a piece of source code you may be looking for, visit our web site at http:/www.ngs.noaa.gov/gps-toolbox. This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada. ? 2002 Wiley Periodicals, Inc.     

The GPSTk: an open source GPS toolkit

Applied Research Laboratories, The University of Texas at Austin (ARL:UT) has established a cross platform open source software project called the GPSTk or the GPS Toolkit. The GPSTk consists of a library and collection of applications that support GPS research, analysis, and development. The code is released under the terms of the Lesser GNU Public License. The GPSTk supports a broad range of functionality. This includes reading and writing observations in standard formats, such as RINEX, BINEX, and SP3, ephemeris evaluation, position determination, receiver autonomous integrity monitoring (RAIM), atmospheric delay modeling, cycle slip detection and correction, and P-code generation. The GPSTk provides the core set of functionality that is used for GPS research and development at ARL:UT. ARL:UT has been involved with satellite navigation since Transit (the precursor to GPS) in the 1960s and is currently conducting research in a wide variety of GPS-related fields, including precise surveys, monitor station networks, and ionospheric studies. The GPSTk is a community-wide resource for all users of GPS and GNSS technology. Participation is welcomed in all areas including: bug reports, new algorithms, suggestions for improvement, and contributions of additional functionality or applications. ARL:UT continually improves the library, shepherds community participation, and is committed to the project’s development and maintenance. The GPS Toolbox is a column dedicated to highlighting algorithms and source code utilized by GPS Engineers and scientists. If you have an interesting program or software package you would like to share with our readers, please pass it along; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here, or to download source code, visit our website at . This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada.     

MATLAB Tools for viewing GPS velocities and time series

Over the past decade, many Global Positioning System (GPS) networks have been installed to monitor tectonic motions around the world. Some of these networks contain hundreds of sites spread across active tectonic margins where the differences in velocities across the network can be 50–100 mm/year. For networks that have been running for a number of years, the uncertainty in the velocity estimates can be less than 1 mm/year. In some cases the vertical motions can also be significant and of importance. Often, the time series of the motions of the GPS sites show complex non-linear behavior, and in all cases the statistical model of the time series is more complex than simple white noise. In this article, we describe a set of Matlab tools developed for use with the GAMIT/GLOBK GPS data analysis system (King 2002; King and Herring 2002) that allow interactive viewing and manipulation of GPS velocities and time series with a Matlab-based graphical user interface (GUI). The formats of the data files used by the tools are specific to GAMIT/GLOBK, but they are simple ASCII files that can be generated from other file formats. The tools are referred to as GGMatlab.The GPS Toolbox is a column dedicated to highlighting algorithms and source code utilized by GPS Engineers and scientists. If you have an interesting program or software package you would like to share with our readers, please pass it along; e-mail it to us at gps-toolbox@ngs.noaa.gov/. To comment on any of the source code discussed here, or to download source code, visit our website at . This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada. For the sidebar, see the Volume 6, Number 4, 2003 issue of the GPS Toolbox column.     

UNB3m_pack: a neutral atmosphere delay package for radiometric space techniques

Several hybrid neutral atmosphere delay models have been developed at the University of New Brunswick. In this paper we are presenting UNB3m_pack, a package with subroutines in FORTRAN and corresponding functions in MatLab which provides neutral atmospheric information estimated using the UNB3m model. The main goal of UNB3m is to provide reliable predicted neutral atmosphere delays for users of global navigation satellite systems (GNSS) and other transatmospheric radiometric techniques. Slant neutral atmosphere delays are the main output of the package, however, it can be used to estimate zenith delays, Niell mapping functions values, delay rates, mapping function rates, station pressure, temperature, relative humidity and the mean temperature of water vapor in the atmospheric column. The subroutines work using day of year, latitude, height and elevation angle as input values. The files of the package have a commented section at the beginning, explaining how the subroutines work and what the input and output parameters are. The subroutines are self-contained, i.e., they do not need any auxiliary files. The user has simply to add to his/her software one or more of the available files and call them in the appropriate way. The GPS Tool Box is a column dedicated to highlighting algorithms and source code utilized by GPS engineers and scientists. If you have an interesting program or software package you would like to share with our readers, please pass it along; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here, or to download source code, visit our website at . This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada.     

Software tools for accessing the GPS Seamless Archive

The Scripps Orbit and Permanent Array Center (SOPAC) has completed development for the UNAVCO community of first-generation GPS Seamless Archive (GSAC) software. The GSAC is a virtual archive composed of an assembly of agencies and investigators exchanging information about their respective GPS-related data holdings in a well defined, cohesive manner. The superset of this published information is collected and ingested into centralized databases administered currently by two data brokers (Retailers), who make the data available to the public in a seamless manner. There are three user interfaces available: the interactive GSAC Wizard, a command-line Unix-style executable called gsac-client, and a front door HTTP service called the GSAC Retailer Service Interface. Each user interface provides access to the data collections of 6 different GPS archives (GSAC Wholesalers) in North America. Together these archives have published more than 2 million GPS data files pertaining to over 10,000 different geodetic monuments. These datasets are composed in large part of data collected by US scientists and their collaborators over the period 1986 to the present in Western North America and other tectonically active regions around the globe, as well as the holdings of two IGS global data centers. In this article, we describe how the three GSAC user interfaces provide the community a powerful set of tools for seamlessly mining information and collecting data files from a distributed network of GPS archives.The GPS Toolbox is a column dedicated to highlighting algorithms and source code utilized by GPS Engineers and scientists. If you have an interesting program or software package you would like to share with our readers, please pass it along; e-mail it to us at gps-toolbox@ngs.noaa.gov. To comment on any of the source code discussed here, or to download source code, visit our website at . This column is edited by Stephen Hilla, National Geodetic Survey, NOAA, Silver Spring, Maryland, and Mike Craymer, Geodetic Survey Division, Natural Resources Canada, Ottawa, Ontario, Canada.     

Introducing HTDP 3.1 to transform coordinates across time and spatial reference frames

The National Geodetic Survey, an office within the National Oceanic and Atmospheric Administration, recently released version 3.1 of the Horizontal Time-Dependent Positioning (HTDP) utility for transforming coordinates across time and between spatial reference frames. HTDP 3.1 introduces improved crustal velocity models for both the contiguous United States and Alaska. The new HTDP version also introduces a model for estimating displacements associated with the magnitude 7.2 El Mayor–Cucapah earthquake of April 4, 2010. In addition, HTDP 3.1 enables its users to transform coordinates between the newly adopted International Terrestrial Reference Frame of 2008 (ITRF2008) and IGS08 reference frames and other popular reference frames, including current realizations of NAD 83 and WGS84. A more convenient format to enter a list of coordinates to be transformed has been added. Users can now also enter dates in the decimal year format as well as the month-day-year format. The new HTDP utility, explanatory material and instructions are available at http://www.ngs.noaa.gov/TOOLS/Htdp/Htdp.shtml.     

弱GPS信号捕获算法的仿真实验研究

针对低信噪比环境下导航的需要,文章对低信噪比环境下弱GPS信号捕获算法进行了分析,重点对相关累加、非相关累加以及多重数据位循环相关累加捕获算法的信号处理流程和算法捕获性能进行讨论。通过特定的硬件装置获得真实的GPS信号,利用Matlab对上述3种常用的弱GPS信号捕获算法进行计算机仿真研究。根据理论分析和仿真结果可以看出,多重数据位循环相关捕获算法更适合检测低信噪比环境下的GPS信号。     

On-line detection of abrupt changes in the carrier-phase measurements of GPS

The detection of cycle slips in carrier-phase data, outliers in phase rate or in code ranges, or any other type of disorder in the measurements of the GPS system, is one of the major quality-control problems that needs to be addressed, especially where GPS is used for real-time applications or for those applications that require continuous and reliable positioning results. This study is concerned with designing algorithms to detect failures or changes of small magnitude, in order to monitor and control the quality of GPS measurements for critical real-time and/or deformation applications. In this regard, the statistical technique known as the cumulative-sum test is described for the detection of abrupt changes in the GPS carrier-phase measurements. Real GPS data have been used to test and evaluate the algorithm. Received: 27 August 1996 / Accepted: 26 February 1997     

惯性导航与卫星导航紧耦合技术发展现状

对紧耦合方案、最优估计滤波算法和硬件开发等几方面进行了总结分析。分析了传统的INS／GPS松组合系统和INS／GPS紧耦合系统的区别；给出了INS／GPS紧耦合系统国内外的发展状况；指出INS／GPS紧耦合系统所涉及的关键技术。     

扩展卡尔曼滤波的安卓手机定位算法研究

随着手机定位的应用越来越多,目前市场中许多APP(Application)都会用到定位功能.但多数APP使用传统的定位算法,不能满足人们实时获取高精度地理位置信息的需求.现阶段对于手机的全球定位系统(GPS)芯片原始数据定位方法的研究较少,因此本文主要对利用手机GPS原始数据定位的可行性及定位算法进行了研究.利用Android 7.0系统提供的应用程序接口获取GPS芯片的原始数据参数,根据手机实用场景的速度特征,分别设计并实现了针对于静态场景的静态卡尔曼滤波和针对低速场景的动态卡尔曼滤波定位算法.通过静态实验以及电动车实验和步行实验的结果表明:与传统的定位算法相比,本文设计的静态卡尔曼滤波和动态卡尔曼滤波定位算法拥有更好的定位结果,更加接近实际行走路线,证明了利用手机GPS原始数据定位的可行性,同时也证明了设计的卡尔曼滤波算法可以提高定位精度,论文的研究结果为实现静态与动态的高精度手机定位算法提供了理论依据.     

基于GPS与GIS集成的车辆导航系统设计与实现

介绍了基于GPS与GIS集成的车辆导航系统设计与实现 ,探讨了导航系统中电子地图的空间数据组织 ,提出了GPS信号与GIS路网数据匹配、快速的邮路选择、最佳路径选择、地图随驾驶方向快速实时旋转技术及语音提示、语音识别技术的使用。     

后向投影算法的地理坐标系下的合成孔径雷达成像

传统的机载合成孔径雷达(SAR)一般依赖于GPS/INS组合系统补偿平台的运动误差,并获得高分辨率的图像。GPS获取的地理坐标(即经度,纬度和高度)需要转换为本地的直角坐标,原始雷达数据在这个直角坐标系下才能引入成像及运动补偿算法进行处理,并获得本地直角坐标系下的图像。这种图像是通过局部坐标描述的,对于其他部门是不通用的,因为其他部门需要的是经过全球地理坐标标绘的图像。本文提出了一种由后向投影算法BP(Back Projection)引出的新的SAR成像算法,它直接在地理坐标下处理,可避免坐标转换的过程。而且生成德图像像素均和地理坐标一一对应,能够很方便地被情报或其他部门使用。而且在仿真试验以及外场试验中,证明了本文算法和常规BP算法成像效果是相当的。     

GPS vector configuration design for monitoring deformation networks

 The performance of geodetic monitoring networks is heavily influenced by the configuration of the measured GPS vectors. As an effective design of the GPS measurements will decrease GPS campaign costs and increase the accuracy and reliability of the entire network, the identification of the preferred GPS vectors for measurement has been highlighted as a core problem in the process of deformation monitoring. An algorithm based on a sensitivity analysis of the network, as dependent upon a postulated velocity field, is suggested for the selection of the optimal GPS vectors. Relevant mathematical and statistical concepts are presented as the basis for an improved method of vector configuration design. A sensitivity analysis of the geodetic geodynamic network in the north of Israel is presented, where the method is examined against two deformation models, the Simple Transform Fault and the Locked Fault. The proposed method is suggested as a means for the improvement of the design of monitoring networks, a common practice worldwide. Received: 30 July 2001 / Accepted: 3 June 2002 Acknowledgments. It is my pleasant duty to thank the Survey of Israel and Dr. E. Ostrovsky for providing the variance–covariance matrix of the G1 network in northern Israel. I would like to thank the reviewers of this paper for their constructive and helpful remarks.     

The activities of the Ionosphere Working Group of the International GPS Service (IGS)

This article is based on a position paper presented at the IGS Network, Data and Analysis Center Workshop 2002 in Ottawa, Canada, 8–11 April 2002, and introduces the IGS Ionosphere Working Group (Iono_WG). Detailed information about the IGS in general can be found on the IGS Central Bureau Web page: http://igscb.jpl.nasa.gov. The Iono_WG commenced working in June 1998. The working group's main activity currently is the routine production of ionosphere Total Electron Content (TEC) maps with a 2-h time resolution and daily sets of GPS satellite and receiver hardware differential code bias (DCB) values. The TEC maps and DCB sets are derived from GPS dual-frequency tracking data recorded with the global IGS tracking network. In the medium- and long-term, the working group intends to refine algorithms for the mapping of ionospheric parameters from GPS measurements and to realize near–real–time availability of IGS ionosphere products. The paper will give an overview of the Iono_WG activities that include a summary of activities since its establishment, achievements and future plans. Electronic Publication     

基于GPS矢量观测信息的姿态确定算法

用于GPS姿态确定的矢量化算法可等价于两级最优问题。第一级把GPS载波相位观测量转换为矢量观测量。第二级是Wahba问题,即从矢量观测量获得最佳姿态解。Wahba问题可用四元数法求解,如QUEST方法。本文采用基于小角度的迭代法求解Wahba问题。在均衡星座或均衡基线务件下,两级最优解亦是全局最优解。实验结果表明迭代解的精度与QUEST解相同。实验中也应用了改进的TRIAD算法以比较两级最优解。     

High-rate GPS clock corrections from CODE: support of 1 Hz applications

GPS zero-difference applications with a sampling rate up to 1 Hz require corresponding high-rate GPS clock corrections. The determination of the clock corrections in a full network solution is a time-consuming task. The Center for Orbit Determination in Europe (CODE) has developed an efficient algorithm based on epoch-differenced phase observations, which allows to generate high-rate clock corrections within reasonably short time (< 2 h) and with sufficient accuracy (on the same level as the CODE rapid or final clock corrections, respectively). The clock determination procedure at CODE and the new algorithm is described in detail. It is shown that the simplifications to speed up the processing are not causing a significant loss of accuracy for the clock corrections. The high-rate clock corrections have in essence the same quality as clock corrections determined in a full network solution. In order to support 1 Hz applications 1-s clock corrections would be needed. The computation time, even for the efficient algorithm, is not negligible, however. Therefore, we studied whether a reduced sampling is sufficient for the GPS satellite clock corrections to reach the same or only slightly inferior level of accuracy as for the full 1-s clock correction set. We show that high-rate satellite clock corrections with a spacing of 5 s may be linearly interpolated resulting in less than 2% degradation of accuracy.     

An adaptive Markov chain algorithm applied over map-matching of vehicle trip GPS data

Markov chains have frequently been applied to match the probable routes with a set of GPS trip data that a pilot vehicle is emitting over a specific graph road network. This class of map- matching (MM) algorithms presently demonstrates and involve statistical and ad-hoc measures to drive the Markov chain transitional probabilities in picking the best route combinations constrained over the graph road network. In this study, we have devised an adaptive scheme to modify the Markov Chain (MC) kernel window as we move along the GPS samples to reduce the mistakes that can happen by the use of narrower MC widths. The measure for temporarily increasing the MC window width is chosen to be the ratio between the geodesic distance of current route to the actual geodesic distance between each pair of GPS samples. This adaptive use of MC has shown to have hardened the results significantly with tolerable computational cost increase. The details of the overall algorithm are depicted by the example routes extracted from various vehicle trips and the results are shown to validate the usefulness of the algorithm in practice.