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goGPS free and constrained relative kinematic positioning with low cost receivers

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goGPS is a software package designed to enhance the accuracy of standalone GPS receivers by exploiting networks of GNSS permanent stations to apply real-time relative positioning, extended Kalman filtering techniques to better model the kinematics of a roving GPS receiver, digital terrain model observations to mitigate the GPS weakness in the vertical direction and, if it is known in advance that the receiver is moving along a predefined path (e.g. a railway), linear paths to constrain the positioning. The principal innovation introduced by goGPS is the possibility to apply kinematic relative positioning in an effective way on low cost single frequency GPS receivers, enhancing their accuracy from the usual 2-4 m up to some decimeters. Though this kind of receivers is the main target for goGPS, also double frequency receivers are supported. goGPS positioning capabilities have been assessed by testing it under different conditions of sky visibility, signal degradation and dynamics of the roving receiver. Since goGPS needs GPS raw observations (i.e. code pseudorange, phase measurement, signal-to-noise ratio, etc.) the u-blox AEK-4T evaluation kit was chosen as a roving receiver, since it provides them. goGPS performance using AEK-4T were compared both with other low cost instruments (eBonTek eGPS 597, TomTom MKII) and with high level professional receivers (Leica GS20 and Leica GPS System 1200). The results show that goGPS managed to get higher accuracy than low cost receivers during all the tests, in some cases obtaining accuracy levels of the same order of magnitude of those obtained by the single frequency professional receiver (Leica GS20). goGPS is developed in a MATLAB environment and it can run either in real-time mode, receiving the low cost receiver data stream on a USB port and the master station data stream through the Internet, or in post-processing mode, reading master and rover RINEX files or goGPS data saved during a real-time session.
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... Next, we process RINEX files to estimate tropospheric parameters using sophisticated open-source GNSS software, called goGPS, version 1.0 Beta, from Geomatics Research and Development s.r.l. -Lomazzo, Italy (Realini, 2009). In the flood area, we identified at least 5 GNSS stations managed by BIG in the INACORS network. ...
... The leading software for processing RINEX data, goGPS. (Realini, 2009), is an open-source software initially developed by Realini (2009) with contributions from the various thesis works by master students, since 2007 at the Geomatics Laboratory of Politecnico in Milano, Como Campus. It is specifically designed to improve the positioning accuracy of low-cost GNSS devices by relative positioning and the Kalman filtering technique. ...
... The leading software for processing RINEX data, goGPS. (Realini, 2009), is an open-source software initially developed by Realini (2009) with contributions from the various thesis works by master students, since 2007 at the Geomatics Laboratory of Politecnico in Milano, Como Campus. It is specifically designed to improve the positioning accuracy of low-cost GNSS devices by relative positioning and the Kalman filtering technique. ...
Article
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This study aims to utilize GNSS for meteorology in Indonesia. With the "goGPS" software, the zenith troposphere delay (ZTD) value is estimated. Calculations in rainy conditions, the ZTD value is converted into a water vapor value (PWV). The research area for the phenomenon of heavy rain occurred at the end of 2019 in Jakarta and its surroundings, which caused flooding on January 1, 2020. According to the Geophysical Meteorology and Climatology Agency (BMKG), the flood's primary cause was high rainfall. Meanwhile, the rainfall at Taman Mini and Jatiasih stations was 335 mm/day and 260 mm/day, respectively. We get an interesting pattern of PWV values for this rain phenomenon. GNSS data processing, the PWV value at five GNSS stations around Jakarta, shows the same pattern even though the average distance between GNSS stations is ~ 30 km. The PWV value appears to increase at noon on December 30, 2019, and the peak occurs in the early hours of December 31, 2019. The PWV value suddenly decreases at noon on January 1, 2020. Next, the PWV value increases again but not as high as at the previous peak. Since January 2, 2020, the PWV value has decreased and remained almost constant until January 4, 2020. In that period, there were two events that the PWV value increased. The PWV value at the first peak is ~ 70 mm, and at the second peak ~ 65 mm. The most significant increase in PWV value was recorded at CJKT stations.
... In this section, we focus on the EKF used with phase and code observations, since this is the most original part of the software. The Kalman filter implemented in goGPS works on double-difference observations with respect to a reference station (Realini 2009). ...
... The user can choose between different weighting options: without weights, as function of elevation of the satellites, as function of C/N0 of the satellites and as a combination of both of them. More details can be seen in (Realini 2009). The initialization of the goGPS KF starts with a first estimation of the rover approximate position by computing three iterations of linearized least squares adjustment on undifferenced code observations, starting from the center of the earth, resulting in a position with an error of some meters. ...
... The initial state covariance matrix is defined as a diagonal matrix in which we will have the position error variances, the velocity variances, the acceleration variances and the estimated variance of the initial ambiguity; it is introduced just on the lines corresponding to visible satellites and can be different from satellite to satellite (Realini 2009). Note that a high velocity variance can be used to model the acceleration of a body that starts moving from a stationary state. ...
Article
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goGPS is a positioning software application designed to process single-frequency code and phase observations for absolute or relative positioning. Published under a free and open-source license, goGPS can process data collected by any receiver, but focuses on the treatment of observations by low-cost receivers. goGPS algorithms can produce epoch-by-epoch solutions by least squares adjustment, or multiepoch solutions by Kalman filtering, which can be applied to either positions or observations. It is possible to aid the positioning by introducing additional constraints, either on the 3D trajectory such as a railway, or on a surface, e.g., a digital terrain model. goGPS is being developed by a collaboration of different research groups, and it can be downloaded from http://www.gogps-project.org. The version used in this manuscript can be also downloaded from the GPS Toolbox Web site http://www.ngs.noaa.gov/gpstoolbox. This software is continues to evolve, improving its functionalities according to the updates introduced by the collaborators. We describe the main modules of goGPS along with some examples to show the user how the software works.
... There is a strong correlation among the elevation angles, C/N0, and residuals, in particular from 13:00 to 19:00 (UTC + 8). Therefore, a comprehensive weighting strategy based on the elevation angles and C/N0 values was employed to weigh the observation values in this study (Realini 2009;Herrera et al. 2016): ...
... where 2 obs is the observation variance, the subscript obs denotes the code and carrier phase measurements, and e is the satellite elevation angle. We used empirical values of A = 30, s0 = 10, s1 = 50, and a = 20 based on Realini (2009). Note that the accuracies of orbit and clock offsets of the BDS GEO satellite are poor. ...
Article
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Multipath effect is one of the main challenges of precise point positioning (PPP) in complex environments. Nowadays, the BeiDou global navigation satellite system (BDS-3) constellation was fully operational. We evaluated the multipath characteristics of BDS-3 open-service signals. The results indicate that the B2a signal had the best anti-multipath performance, and B1C signal had the worst capability. Since BDS-3 satellites with different orbital types have different orbital repeat time, the traditional method based on multipath time-domain repeatability is complicated to alleviate the multipath error on BDS-3 satellites. In contrast, the multipath spatial-domain repeatability method does not need to calculate the orbital repeat times and is only related to the position of the satellite in the sky. It has the advantages of simple algorithm and easy implementation. We selected a multipath hemispherical map (MHM) and a MHM based on trend-surface analysis (T-MHM) to evaluate the effects of BDS-3 PPP multipath correction. The positioning results for the inclined geosynchronous orbit (IGSO) and medium earth orbit (MEO) satellites, which were separately modeled and corrected, are slightly better than those obtained when they were modeled and corrected together. Compared with the uncorrected multipath, the positioning accuracy of B1I/B3I and B1C/B2a ionospheric-free (IF) combinations using the MHM can be improved by 52.7% and 51.6% and the convergence time can be shortened by 48.6% and 57.5%, respectively. The positioning accuracy of B1I/B3I and B1C/B2a IF combinations using the T-MHM can be improved by 67% and 66.9% and the convergence time can be shortened by 69.3% and 76.5%, respectively. The T-MHM introduces trend-surface analysis to model the spatial variation of the multipath inside the grid, which effectively alleviates high-frequency and low-frequency multipath. This study is of great significance for further improvements to the application of BDS-3 in complex environments.
... In literature, few models, based on both and / , are available, one of which is introduced in [24] and is shown below: ...
... The measured / is compared with the threshold ; if / ≥ , the measurement is fully exploited into the solution (weight is set to 1), being considered sufficiently accurate, otherwise the measurement is de-weighted according to (14). The parameters in (13) and (14) have been determined empirically in [24]. In this work, this model is shortly indicated as 3. ...
... As aforementioned in Section 4.3.2, a measurement weighting scheme is conducted in this thesis to quantify the accuracy of the measurements in different situations. To reflect the differences in measurements accuracy in different environments, the predefined value of the which is the standard deviation of the GNSS code observation at the zenith, is set to different practical values under different environmental conditions [144]. The values selected in this thesis are described in Table 6-2. ...
Thesis
Precise positioning with a stand-alone GPS receiver or using differential corrections is known to be strongly degraded in an urban or sub-urban environment due to frequent signal masking, strong multipath effect, frequent cycle slips on carrier phase, etc. The objective of this Ph.D. thesis is to explore the possibility of achieving precise positioning with a low-cost architecture using multiple installed low-cost single-frequency receivers with known geometry whose one of them is RTK positioned w.r.t an external reference receiver. This setup is thought to enable vehicle attitude determination and RTK performance amelioration. In this thesis, we firstly proposed a method that includes an array of receivers with known geometry to enhance the performance of the RTK in different environments. Taking advantage of the attitude information and the known geometry of the installed array of receivers, the improvement of some internal steps of RTK w.r.t an external reference receiver can be achieved. The navigation module to be implemented in this work is an Extended Kalman Filter (EKF). The performance of a proposed two-receiver navigation architecture is then studied to quantify the improvements brought by the measurement redundancy.This concept is firstly tested on a simulator in order to validate the proposed algorithm and to give a reference result of our multi-receiver system’s performance. The pseudo-range measurements and carrier phase measurements mathematical models are implemented in a realistic simulator. Different scenarios are conducted, including varying the distance between the 2 antennas of the receiver array, the satellite constellation geometry, and the amplitude of the noise measurement, in order to determine the influence of the use of an array of receivers. The simulation results show that our multi-receiver RTK system w.r.t an external reference receiver is more robust to noise and degraded satellite geometry, in terms of ambiguity fixing rate, and gets a better position accuracy under the same conditions when compared with the single receiver system. Additionally, our method achieves a relatively accurate estimation of the attitude of the vehicle which provides additional information beyond the positioning.In order to optimize our processing, the correlation of the measurement errors affecting observations taken by our array of receivers has been determined. Then, the performance of our real-time single frequency cycle-slip detection and repair algorithm has been assessed. These two investigations yielded important information so as to tune our Kalman Filter.The results obtained from the simulation made us eager to use actual data to verify and improve our multi-receiver RTK and attitude system. Tests based on real data collected around Toulouse, France, are used to test the performance of the whole methodology, where different scenarios are conducted, including varying the distance between the 2 antennas of the receiver array as well as the environmental conditions (open sky, suburban, and constrained urban environments). The thesis also tried to take advantage of a dual GNSS constellation, GPS and Galileo, to further strengthen the position solution and the reliable use of carrier phase measurements. The results show that our multi-receiver RTK system is more robust to degraded GNSS environments. Our experiments correlate favorably with our previous simulation results and further support the idea of using an array of receivers with known geometry to improve the RTK performance.
... In a relative positioning system, a position vector is considered the center of the system, which means that the position vector between the reference and rover receiver is calculated through the CPDGPS method. Some methods based on a short baseline were presented by Realini [5], Comstock [6], and Zheng [7], who worked on CPDGPS and integer ambiguity. Octavian [8] described an alternative precise, cost-effective positioning system of professional-and geodetic-grade receivers. ...
Article
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The Global Positioning System (GPS) is currently used in many geodetic applications to obtain precise positions within a centimeter, or even within a millimeter. Generally, such a level of accuracy can be obtained by performing complex processing on expensive receivers and antennas. Such high-cost devices can be replaced by low-cost, single-frequency GPS receivers to obtain precise positions. To do so, in this paper, Carrier Phase (CP)-based relative algorithms are successfully implemented on a CUDA-enabled embedded board (the Jetson TK1) with two low-cost GNNS receivers. A CUDA-enabled graphics processing unit (GPU) is a highly parallel structure that makes efficient and faster CP-based algorithms and that can process large blocks of data in parallel. Our results from field measurements clearly show that the positioning performance of a Rover with respect to the Base receiver reached the centimeter level. Therefore, this work shows the possibility of accurately estimating the position of a receiver using low-cost hardware-based RTK algorithms.
... The main software for extracting RINEX data, namely goGPS. (Realini, 2009) Some of the research results using goGPS, among others, Realini et al. (2012) stated that goGPS could work in either real-time or post-processing, by getting raw GPS data in the input and providing position (i.e., coordinates) in the output. Herrera et al. (2016) goGPS published under a free and open-source license, goGPS can process data collected by any recipient but focuses on the treatment of observations by low-cost recipients. ...
Article
The tropospheric delay is an essential source of error for positioning using the Global Navigation Satellite System (GNSS). Scientific applications of GNSS positioning such as the study of earth crust deformation and earthquake prediction require high accuracy in positioning, an analysis of tropospheric delay calculations is needed to improve the accuracy of GNSS positioning. One part of the tropospheric delay is Zenith tropospheric delays (ZTD), which are estimated using the Precise Point Positioning (PPP) method. ZTD estimates can be beneficial for meteorological applications, for example, is the estimation of water vapor levels in the atmosphere from the estimated ZTD. We use GNSS data from the BAKO station in Cibinong and JOG2 station located in Yogyakarta. The GNSS data format is an Independent Exchange Receiver (RINEX), which we extracted using the sophisticated open-source GNSS software, called goGPS version 1.0 Beta from Geomatics Research and Development s.r.l.-Lomazzo, Italy. We validate the results of the extraction process with two international tropospheric products from International GNSS Services (IGS) with commercial software Bernese version 5 and the University of Nevada Reno (UNR) with software from NASA Jet Propulsion Laboratory (JPL) namely GIPSY / OASIS II. Epoch in this study, we use days of the year (DOY) 022-025 / 22-25 January representing the rainy season and DOY 230-233 to coincide on August 17-20 representing the dry season 2018. Our results obtained ZTD values both in January and August, and the two BAKO and JOG2 stations were consistent and worked well at different times and stations. RMS throughout DOY, both at BAKO and JOG2 stations, show small values <2 mm. The RMS value is relatively small, meaning that the troposphere estimation process with goGPS shows a good agreement because it is almost the same as the international troposphere products from UNR and IGS. This means that the ZTD estimation process from goGPS software can be an alternative to paid software. The range of ZTD values in January tends to be higher than in August, meaning the value of ZTD has a strong correlation with changes in the rainy and dry seasons, this shows that ZTD can be useful for meteorological purposes.
... Table 1 performs the parameters comparison between the geodetic and low cost receivers, showing different characteristics of these two receivers. Realini et al. carried out a series of research on low cost receiver with goGPS, and verified that location accuracy of single frequency and low cost receiver processed by goGPS has been greatly improved [1][2][3]. Takasu et al. had evaluated the performance of low cost receivers and achieved precise result with low cost receivers by RTKLIB [4]. Marco et al. studied on the landslide monitoring using the low cost receiver and investigated the effect of baseline length on the result [5,6]. ...
Chapter
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In the satellite navigation and positioning process, the performance of the receiver directly impacts on the quality of observation data, and affects the positioning accuracy ultimately. Therefore, the receiver is sufficiently important for the whole navigation and positioning process. Deformation monitoring belongs to precise engineering survey and it often needs to reach the millimeter-level accuracy, so that the geodetic receiver with excellent performance and high price is often used in this survey. Under this background, improving the positioning accuracy of low cost receiver and applying it to deformation monitoring can effectively reduce the engineering cost, which has great practical significance and research value. This study is based on the low cost receiver EVK-M8T from ublox company. Firstly, the receiver performance is evaluated from signal to noise ratio (SNR), receiver clock and accuracy of standard point positioning (SPP) through comparing with geodetic receiver Trimble NetR9. Then through the experiment simulation of deformation monitoring, the feasibility of deformation monitoring using low cost receiver is analyzed. The numerical results show that the location accuracy of low cost receiver can basically keep in millimeter level when the observation period reaches more than 2 h, and it can correctly detect the movement of the point. Hence low cost receiver can be applied to the deformation monitoring under the premise of improving its stability.
... The implementation and comparison of the two approaches is currently in progress. Many parts of the needed processing software are already available as Free and Open Source Software (FOSS) programs or libraries, like goGPS ("goGPS Project", 2016;Realini, 2009;Realini & Reguzzoni, 2013) and RTKLib ("RTKLib", 2016;Takasu & Yasuda, 2009); for the MEP purposes, they needed to be tuned and embedded in one automatized software. Correspondingly, all the new implemented software will be freely published according to FOSS standards. ...
Chapter
The increasing use of technologies like smart phones and mobile apps enables people to be actively involved in collecting data that can be the base of useful services to the whole citizenship. In the realm of volunteer data collection, this chapter addresses the problem of mobility and accessibility limitations for vulnerable citizens in today's cities. The MEP (Maps for Easy Paths) project proposes a set of tools and mobile apps for the enrichment of geographical maps with information about accessibility of urban pedestrian pathways, targeted at people with mobility problems. Different issues are considered and discussed in this chapter, including: the problem of collecting data of a user's route and of reconstructing it with novel sensor fusion techniques; the problem of correcting the positions obtained from low-cost GNSS receivers of mobile devices; the need of usable and accessible applications for the fruition of the collected data suitable for the target users.
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Conference Paper
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Alpine) e il Politecnico di Milano hanno intrapreso lo sviluppo di un Servizio Regionale di Posizionamento per la Lombardia: il Servizio prevede la realizzazione di una rete di stazioni permanenti GPS e di un centro di analisi, controllo e distribuzione di dati e prodotti. Il Servizio fornirà all'utenza finale, privata e pubblica, gli strumenti essenziali per le applicazioni di rilievo finalizzate al monitoraggio e alla pianificazione del territorio, alla produzione e all'aggiornamento di cartografia; inoltre svolgerà attività di ricerca negli ambiti propri del posizionamento satellitare supportato da reti di stazioni permanenti. La rete di stazioni permanenti si comporrà di 19 stazioni, posizionate in modo che ogni punto del territorio regionale disti dalla più vicina non più di 35 chilometri; il centro di elaborazione sarà dimensionato, sia per risorse umane sia per risorse tecnologiche, in modo da garantire la distribuzione di servizi e l'attività di ricerca per l'evoluzione degli stessi. Nel presente lavoro vengono illustrate le finalità, la struttura e le fasi di realizzazione previste per il Servizio. Abstract.
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ABSTRACT The accuracy of today’ s RTK is limited by the distance dependent errors from orbit, ionosphere and troposphere as well as station dependent influences like multipath and antenna phase center variations. The basic idea of Geo++, GNSMART (GNSS - State Monitoring And Representation Technique) is to analyze the data from a reference station network to estimate and represent the
Conference Paper
A positioning service based on a GNSS network of permanent stations materializes the global reference frame and distributes it to its users, by distributing the estimated coordinates of the permanent stations, their raw data and other network products. In these years, positioning services are under development in Italy; typically they are designed, created and managed at the spatial scale of the Italian Regions. The first of them, located in Lombardia Region, has been designed and implemented starting from 2003: from January 2006 it is distributing data and products for real time and post processing applications. Three data quality checks and coordinate monitoring processes are performed, at three different latency levels. The first check is directly managed by the software that acquires RTCM streams from the stations to compute the real time network products. The final monitoring is made at a completely different latency and is finalized to the estimation of the permanent stations coordinates; it is computed by the daily adjustment of the Lombardia network within the IGS network, by constraining IGS stations to their published coordinates and by using the final IGS products; the final adjustment is computed with a two weeks latency: the solutions are analyzed and stored to check discontinuities and infer trends in the coordinates; moreover suitable quality indexes are extracted from the adjustment outputs in order to check the data quality: the exceeding of assigned thresholds by the indexes is automatically signalized. A further adjustment is performed to check both the data quality and the coordinates stability in near real time. It runs daily, immediately after midnight, by using ultra rapid IGS ephemerides and only Lombardia stations: also in this case the data quality is checked by analyzing the elaboration outputs; the coordinates stability is checked by comparing the results with the coordinates estimated in the final monitoring. The final monitoring is operating from January 2006, while the near real time quality has started in the last months. At first, the paper describes the Lombardia positioning service implementation; then, the choices adopted, the procedures implemented and the results obtained in one year of monitoring are discussed; at last the near real time quality check is described.