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This paper presents an innovative and cost-effective solution for the absolute localization of mobile robots using ultrasound beacons. The proposed system addresses the challenge of precise positioning within a controlled environment by employing Differential Time-of-Flight (ToF) measurements to determine the relative distances between the robot and optimally placed beacons. Unlike other ToF methods that require synchronization pulses, the proposed approach eliminates this requirement, significantly simplifying the setup and reducing system complexity. Furthermore, the system achieves a higher sampling rate than conventional synchronization-based systems, enhancing real-time performance. Detailed analysis and simulation demonstrate the system's ability to provide accurate and reliable localization. The results highlight the potential for broad application in various robotic environments, offering a robust solution for absolute positioning without complex synchronization strategies. This work underscores the advantages of using ToF measurements with ultrasound beacons and contributes to the ongoing development of efficient and cost-effective robotic localization systems. [ABSTRACT FROM AUTHOR]

In challenging environments such as disaster aid or forest rescue, unmanned aerial vehicles (UAVs) have been hampered by inconsistent or even denied global navigation satellite system (GNSS) signals, resulting in UAVs becoming incapable of operating normally. Currently, there is no unmanned aerial vehicle (UAV) positioning method that is capable of substituting or temporarily replacing GNSS positioning. This study proposes a reliable UAV top-down absolute positioning method (RTAPM) based on a monocular RGB camera that employs joint optimization and visual–inertial assistance. The proposed method employs a bird’s-eye view monocular RGB camera to estimate the UAV’s moving position. By comparing real-time aerial images with pre-existing satellite images of the flight area, utilizing components such as template geo-registration, UAV motion constraints, point–line image matching, and joint state estimation, a method is provided to substitute satellites and obtain short-term absolute positioning information of UAVs in challenging and dynamic environments. Based on two open-source datasets and real-time flight experimental tests, the method proposed in this study has significant advantages in positioning accuracy and system robustness over existing typical UAV absolute positioning methods, and it can temporarily replace GNSS for application in challenging environments such as disaster aid or forest rescue.

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The absolute positions of shearers on advancing coal faces are requisite for providing references for adaptive mining combined with geological models. Common coalmine localization techniques (e.g. UWB, INS, etc.) are not fully applicable to adaptive mining due to their drifting error or the messy environment. The gyro robotic total station (RTS) is versatile and precise in measuring coordinates in coal mines, while its conventional usage is of low automation and poor timeliness, impeding its application on mining faces. This article proposed an automated gyro RTS system for real-time absolute positioning on fully mechanised coal faces. The measuring process was changed to fit mining requirements, and a new state-transferring model was used to automate it. Programs were developed and installed in available instruments, forming a prototype. Field experiments were carried out on a simulative working face, verifying the system's accuracy and applicability. Results show that the relative positioning error is better than 2.6143×10-4, which meets the demand of advancing faces. The error of the gyro is estimated at 55.5187", justifying its nominal indicators. To sum up, the automated gyro RTS system proposed in this paper can offer real-time and accurate absolute positions of equipment on working faces, supporting adaptive mining combined with the geological model. [ABSTRACT FROM AUTHOR]

The employment of unmanned aerial vehicles (UAVs) has greatly facilitated the lives of humans. Due to the mass manufacturing of consumer unmanned aerial vehicles and the support of related scientific research, it can now be used in lighting shows, jungle search-and-rescues, topographical mapping, disaster monitoring, and sports event broadcasting, among many other disciplines. Some applications have stricter requirements for the autonomous positioning capability of UAV clusters, requiring its positioning precision to be within the cognitive range of a human or machine. Global Navigation Satellite System (GNSS) is currently the only method that can be applied directly and consistently to UAV positioning. Even with dependable GNSS, large-scale clustering of drones might fail, resulting in drone cluster bombardment. As a type of passive sensor, the visual sensor has a compact size, a low cost, a wealth of information, strong positional autonomy and reliability, and high positioning accuracy. This automated navigation technology is ideal for drone swarms. The application of vision sensors in the collaborative task of multiple UAVs can effectively avoid navigation interruption or precision deficiency caused by factors such as field-of-view obstruction or flight height limitation of a single UAV sensor and achieve large-area group positioning and navigation in complex environments. This paper examines collaborative visual positioning among multiple UAVs (UAV autonomous positioning and navigation, distributed collaborative measurement fusion under cluster dynamic topology, and group navigation based on active behavior control and distributed fusion of multi-source dynamic sensing information). Current research constraints are compared and appraised, and the most pressing issues to be addressed in the future are anticipated and researched. Through analysis and discussion, it has been concluded that the integrated employment of the aforementioned methodologies aids in enhancing the cooperative positioning and navigation capabilities of multiple UAVs during GNSS denial.

During the last decade Global Positioning System (GPS) Continuous Operating Reference Stations networks have become a new important data source for meteorology. This has dramatically improved the ability to remotely sense the atmosphere under the influence of severe mesoscale and synoptic systems. The zenith tropospheric delay (ZTD) is one of the atmospheric variables continuously observed, and its horizontal variations, the horizontal tropospheric gradients, are routinely computed nowadays within the dual‐frequency GPS processing, but their interpretation and relationship with the weather is still an open question. The purpose of this paper is to contribute in this direction by studying the effect that Hurricane Harvey had on the spatial and temporal behavior of the ZTDs and gradients, when it reached Texas coast, during 18–31 August 2017. The results show that ZTD time series present a clear and rapid increase larger than 10 cm in a few hours when the hurricane reached the area. Gradients behaviors show that the hurricane also produced significant changes on them, since the magnitude and predominant directions before and after the hurricane arrived are completely different. Noticeably, the gradient vectors before the landing are consistently related to the horizontal winds and pressure fields. In this manuscript we demonstrate that the ZTD gradients can show a consistent signature under severe weather events, strongly suggesting their potential application for short‐term weather forecasting.

In this study, the potential of PPP (Precision Point Positioning) method in crustal deformation studies was investigated with the help of relative GNSS (Global Navigation Satellite System) analyses. For this purpose, data of six GNSS stations, three (GIRS, SINP and ZONG) of which are located to the north of the North Anatolian Fault (NAF) zone and the other three (RHIY, ANKR and BILE) are located to the south of the NAF zone, were obtained and analyzed between the years of 2011-2018 (8 years long). The analyzes were carried out by means of the CSRS online service for the PPP method and the GAMIT / GLOBK V10.7 academic GNSS analysis software for the relative positioning technique. The obtained coordinates are analyzed with the help of Kalman filter to estimate the velocities of each station for the North, East and Up components as fixed on the ORID IGS (International GNSS Service) station which located on the Eurasian plate. It was found that the 3D positioning error calculated from the velocity differences between the both methods ranged from 0.1 mm to 2.4 mm levels. Thus, it is concluded that PPP method can be used successfully in crustal deformation studies. [ABSTRACT FROM AUTHOR]

In recent years GNSS measurements techniques obtained a majority role in civil engineering and other technical fields. An example of this is the monitoring of both natural phenomena and manmade constructions. The main advantages of satellite positioning, as opposite to classical surveying techniques like levelling or total stations, are continuous long term observations and economic advantage, due to the lack of measurement crew. Currently, apart from GPS, other satellite systems in use like GLONASS or Galileo are becoming more important. Together with development of GNSS measurements for satellite positioning in open areas, also urban and mountainous areas can be measured. This kind of areas was excluded from measurements with single GNSS system, due to the lack of the required minimum number of visible satellites. Multi-GNSS (hybrid, integrated - usage of more than one satellite navigation system in measurements) positioning, currently providing more than 80 active satellites, opens new grounds for satellite measurements. Among measurement methods PPP is the most developing one since the beginning of 21st century. Main PPP advantages are: independence from reference station, lack of limitation of use to certain areas and global coverage with consistent, homogenous solutions. The paper shows the results of 90-days continuous static observations processed with the usage of PPP technique on simulated different sky view conditions. Measurements were made on points with known coordinates as a construction simulation. The data were processed in three modes: GPS-only, GLONASS-only and hybrid GNSS (GPS+GLONASS) using three different elevation cut-off angles. Accuracy analyses were carried out on the basis of final, daily EPN solutions at the observation time.

In this study, the accuracy of Precise Point Positioning (PPP) method was investigated. For this purpose, a microgeodetic network containing 5 stations was established and 8-hour GNSS Global Navigation Satellite System (GNSS) sessions for three consecutive days were performed. At the same time, the baselines between the stations in this network were measured by Electronic Distance Meter (EDM) and the height differences are measured by the geometric leveling method. The results obtained from classical terrestrial measurements, which are considered to be highly accurate (3 mm in horizontal and few mm invertical), were compared with the results of PPP and the relative GNSS methods. As a result of the comparisons, it was seen that the values obtained from the relative GNSS analysis approximated with the classical method with the levels of 1-6 mm in the horizontal and 10-20 mm in the vertical direction. For the PPP method, it was seen that the same values varied between 1-28 mm in horizontal and 5-8 cm in the vertical component. The standard deviation values of these changes were determined as ± 2.20 mm in horizontal and ± 16.46 mm in vertical for the relative positioning technique and ± 11.43 mm in the horizontal and ± 59.48 mm in vertical component for PPP method. [ABSTRACT FROM AUTHOR]

During the last decade Global Positioning System (GPS) Continuous Operating Reference Stations networks have become a new important data source for meteorology. This has dramatically improved the ability to remotely sense the atmosphere under the influence of severe mesoscale and synoptic systems. The zenith tropospheric delay (ZTD) is one of the atmospheric variables continuously observed, and its horizontal variations, the horizontal tropospheric gradients, are routinely computed nowadays within the dual‐frequency GPS processing, but their interpretation and relationship with the weather is still an open question. The purpose of this paper is to contribute in this direction by studying the effect that Hurricane Harvey had on the spatial and temporal behavior of the ZTDs and gradients, when it reached Texas coast, during 18–31 August 2017. The results show that ZTD time series present a clear and rapid increase larger than 10 cm in a few hours when the hurricane reached the area. Gradients behaviors show that the hurricane also produced significant changes on them, since the magnitude and predominant directions before and after the hurricane arrived are completely different. Noticeably, the gradient vectors before the landing are consistently related to the horizontal winds and pressure fields. In this manuscript we demonstrate that the ZTD gradients can show a consistent signature under severe weather events, strongly suggesting their potential application for short‐term weather forecasting. Key Points: Major hurricane over dense GPS network gives unique opportunity to study ZTD gradientsThe ZTD gradients show changes in orientation and magnitude when synoptic front approaches [ABSTRACT FROM AUTHOR]

Since many years, the GNSS has been regarded by the meteorological community as one of the systems for atmospheric water vapour remote sensing. Time series of wet delays, estimated as by-products of accurate positioning, have been assimilated into numerical weather prediction models. However, a dedicated use the system for water vapour monitoring is still under investigation. Ad hoc dense networks have been designed and implemented to collect data at a high spatial resolution, baseline lengths lower than 10 km, with the aim of describing the high spatial and temporal variability of tropospheric water vapour. Within this framework, the paper reports a study on how the positioning strategy affects the estimated coordinates and tropospheric parameters. The study was conducted on the data collected by an experimental network of geodetic receivers, used as single or dual frequency ones. More specifically, investigations were made on the use of L1-only or iono-free combinations in differential positioning of receivers 100 to 10 km apart, finding that L1-only data provide more accurate results. Therefore, comparisons between local coordinates and ZWD obtained from relative and absolute positioning were performed to provide the statistics of the differences; the agreement between the results for short baselines is always better than 1 cm standard deviation. In order to assess the differences in the results that can be obtained from the two strategies when applied to the same observation set, a further comparison was carried out in terms of baseline components and ZWD increments. It results that, even for dense networks, the differential approach produces accurate results without losing information compared to the absolute one. [ABSTRACT FROM AUTHOR]

The new generation of Android smartphones is equipped with GNSS chips capable of tracking multi-frequency and multi-constellation data. In this work, we evaluate the positioning performance and analyze the quality of observations collected by three recent smartphones, namely Xiaomi Mi 8, Xiaomi Mi 9, and Huawei P30 pro that take advantage of such chips. The analysis of the GNSS observation quality implies that the commonly employed elevation-dependent function is not optimal for smartphone GNSS observation weighting and suggests an application of the C/N0-dependent one. Regarding smartphone code signals on L5 and E5a frequency bands, we found that they are characterized with noticeably lower noise as compared to E1 and L1 ones. The single point positioning results confirm an improvement in the performance when the weights are a function of the C/N0-rather than those dependent on the satellite elevation and that a smartphone positioning with E5a code observations significantly outperforms that with E1 signals. The latter is expressed by a drop of the horizontal RMS from 8.44 m to 3.17 m for Galileo E1 and E5a solutions of Xiaomi Mi 9 P30, respectively. The best positioning accuracy of multi-GNSS single-frequency (L1/E1/B1/G1) solution was obtained by Huawei P30 with a horizontal RMS of 3.24 m. Xiaomi Mi 8 and Xiaomi Mi 9 show a horizontal RMS error of 4.14 m and 4.90 m, respectively.

In the absence of obstacles, a GPS device is generally able to provide continuous and accurate estimates of position, while in urban scenarios buildings can generate multipath and echo-only phenomena that severely affect the continuity and the accuracy of the provided estimates. Receiver autonomous integrity monitoring (RAIM) techniques are able to reduce the negative consequences of large blunders in urban scenarios, but require both a good redundancy and a low contamination to be effective. In this paper a resampling strategy based on bootstrap is proposed as an alternative to RAIM, in order to estimate accurately position in case of low redundancy and multiple blunders: starting with the pseudorange measurement model, at each epoch the available measurements are bootstrapped-that is random sampled with replacement-and the generated a posteriori empirical distribution is exploited to derive the final position. Compared to standard bootstrap, in this paper the sampling probabilities are not uniform, but vary according to an indicator of the measurement quality. The proposed method has been compared with two different RAIM techniques on a data set collected in critical conditions, resulting in a clear improvement on all considered figures of merit. [ABSTRACT FROM AUTHOR]

This paper mainly proposes absolute positioning instruments using camera positioning system and compass.The absolute positioning systems are used to estimate absolute position and orientation errors combined with estimated position and orientation from differential odometry integrated with gyroscope to calculate absolute position and orientation of mobile robot. In the method, the indirect Kalman filter is used to estimate absolute position and orientation errors and the estimated errors are fed back to odometry system, and also estimates some parameter errors to correct odometry system and gyroscope error. The simulation and experimental results show the estimated position and orientation of odometry system integrated with gyroscope, systematic errors of odometry system and gyroscope, absolute position from the camera positioning system and absolute orientation from compass compared with odometry system integrated with gyroscope.

In this paper, we propose a framework referred to as “geodetic synthetic aperture radar (SAR) tomography” that fuses the SAR imaging geodesy and tomographic SAR inversion (TomoSAR) approaches to obtain absolute 3-D positions of a large amount of natural scatterers. The methodology is applied on four very high resolution TerraSAR-X spotlight image stacks acquired over the city of Berlin. Since all the TomoSAR estimates are relative to the same reference point object whose absolute 3-D positions are retrieved by means of stereo SAR, the point clouds reconstructed using data acquired from different viewing angles can be geodetically fused. To assess the accuracy of the position estimates, the resulting absolute shadow-free 3-D TomoSAR point clouds are compared with a digital surface model obtained by airborne LiDAR. It is demonstrated that an absolute positioning accuracy of around 20 cm and a meter-order relative positioning accuracy can be achieved by the proposed framework using TerraSAR-X data. [ABSTRACT FROM AUTHOR]

This article aims to improve the absolute accuracy of an individual industrial robot by means of integrating itself with the workspace Measuring and Positioning System, which is currently under development at Tianjin University, China. We found that the absolute positioning error persists in the robot base frame, whereas the errors, both in position and orientation, can be reduced by changing the reference frame from the robot to the integrated metrology system, that is, the workspace Measuring and Positioning System. What it needs more is several additional corrective movements. And this correction work just needs roughly calibrated parameters between the robot frame and the workspace Measuring and Positioning System frame. To validate it, we present the experiment which demonstrates that the absolute error of the industrial robot can be less than 0.2 mm by virtue of the workspace Measuring and Positioning System and the convergent corrective movements. Aiming to explain the results, this study deduces the mathematical model in detail about the integration of the robot with the workspace Measuring and Positioning System. The model explains why the integration of the robot with the workspace Measuring and Positioning System applies. First, the model tells that there exists a low requirement, that is, the tolerable rough level of the parameters between the robot frame and the workspace Measuring and Positioning System frame, for assuring the convergence of the corrective movements. Second, the relationship among the relevant factors in the corrective process is given. Finally, besides the workspace Measuring and Positioning System, this model is of general significance for any available metrology systems with which the industrial robot can integrate, and it may also provide theoretical instructions for the improvement of the robot off-line programming, that is, the robot can work at a higher accuracy provided by the integrated metrology system. [ABSTRACT FROM PUBLISHER]

A new strategy to realize precise absolute positioning for a single-frequency user is presented. In the presented strategy, the receiver clock and ambiguities are removed using the satellite- and epoch-differenced (SDED) algorithm. As a further development of the SDED algorithm, a regional augmentation network is used to generate the SDED atmospheric delays at the user. The weakened mathematic property due to the epoch-differenced operation is improved by adding the generated atmospheric delays and applying the robust estimation. To test the new approach, the 24-h data at 5 Continuous Operation Reference Station (CORS) stations in Shanghai is processed. The results show a more than 96% success rate, defined as the case where three directions achieve the desired positioning accuracy of 10 cm, when the observation is longer than 20 min. The 20-min static results show that the new method can reach an accuracy of 3.42, 4.76 and 9.26 cm in the North, East and Up directions, respectively. An experiment was carried out to assess the kinematic positioning. The results show that the kinematic positioning accuracy is 4.11, 5.31 and 4.05 cm in the north-south, east-west and height directions, respectively. [ABSTRACT FROM AUTHOR]

As of this writing, there are two popular methods to perform precise surveying using the single dual-frequency Global Positioning System (GPS) receiver. One is the Real-Time Kinematic (RTK) technique. The other is the Precise Point Positioning (PPP) technique. The RTK technique requires GPS surveyors to have at least one GPS base station while the PPP technique needs a long observation period to resolve the carrier-phase ambiguities. This paper proposes a new, fast method that can conduct precise kinematic surveying using a single dual-frequency GPS receiver, overcoming the aforementioned problems. This new method, Absolute Plus Loop-based Accumulated-solution Time-relative (APLAT), combines the GPS absolute-positioning method and a loop-based accumulated-solution time-relative positioning method. In this APLAT method, the kinematic surveying trajectory must form a loop. The coordinates of the start-point of the loop can be precisely determined using the absolute positioning function of APLAT by making two short sessions of static observations. This function is useful if no control-point is available in the kinematic surveying. The relative positions of other kinematic surveying points in the loop are determined using the function of loop-based accumulated-solution time-relative GPS positioning. The integration of the absolute and the relative positioning functions allows kinematic surveying to precisely determine the absolute coordinates of each surveyed point in the loop. To determine the absolute coordinates of the start-point of a loop, only two short sessions (5 min each in this study) of static GPS observations (prior to starting and after completing the loop surveying) are required. The results of extensive absolute-positioning tests show that 3D-positioning standard deviation about 7 cm and root-mean-square (RMS) error about 13.4 cm can be achieved when the loop-duration is in the range of 40-80 min. Too short or long a loop-duration may degrade the absolute-positioning accuracy. Results from various relative positioning tests using the loop-based accumulated-solution time-relative method indicate that relative-positioning RMS errors of 1.3 cm, 2.6 cm, and 8.8 cm can be obtained for loop durations of 20 min, 40 min, and 60 min, respectively. This new APLAT method offers a new, fast, and precise (RMS error of 12 cm for absolute and RMS error of 8.8-cm relative positioning for 60-min loop duration) kinematic surveying method that is able to meet many GPS surveying and mapping requirements. This is particularly useful for postmission data processing in circumstances where single-base-station RTK or network RTK service is not available. In this study, the final precise-orbit and precise-satellite-clock data from the International GNSS Service are used to mitigate these errors. At present, this method is useful just for postmission applications, but it offers the flexibility of using absolute-positioning or relative-positioning function only, depending upon the specific surveying and mapping conditions and requirements. This method is a good complement to the PPP and RTK precise-positioning techniques currently in use. Due to the increasing spatial decorrelation of error sources, the positioning accuracy may degrade as the maximum spatial distance (approximately between the loop start-point and the loop middle-point) increases. [ABSTRACT FROM AUTHOR]

This paper mainly proposes absolute positioning instruments using camera positioning system and compass.The absolute positioning systems are used to estimate absolute position and orientation errors combined with estimated position and orientation from differential odometry integrated with gyroscope to calculate absolute position and orientation of mobile robot. In the method, the indirect Kalman filter is used to estimate absolute position and orientation errors and the estimated errors are fed back to odometry system, and also estimates some parameter errors to correct odometry system and gyroscope error. The simulation and experimental results show the estimated position and orientation of odometry system integrated with gyroscope, systematic errors of odometry system and gyroscope, absolute position from the camera positioning system and absolute orientation from compass compared with odometry system integrated with gyroscope. [ABSTRACT FROM AUTHOR]

The French Transportable Laser Ranging System (FTLRS) was deployed in the calibration site of satellite radar altimeters in Corsica over the 2002 and 2005 campaigns. The paper describes the different steps of SLR data processing. The average arcs RMS obtained are about 1-2 cm for Lageos-1&-2, Starlette and Stella satellites; it is shown that the best results of satellite orbits determination and geocentric positioning are obtained with Eigen-Grace03s gravity model. The difference of FTLRS absolute 3D positioning, between 2002 and 2005, of about 7.7 mm (i.e., 2.6 mm/yr) is less than residual errors of ITRF2005 velocities (of about 4.3 mm/yr). [ABSTRACT FROM AUTHOR]

This paper presents the method and the results of investigations to determine the position vector of a static or moving vehicle using the Global Positioning System (GPS) in the absolute (point) positioning mode with and without selective availability. Starting from the basic positioning scheme with code observation, the most accurate positioning strategy using the phase is described. The main strategy for the highest accuracy absolute positioning is to estimate GPS satellite clock errors independently, thus obviating the between-station differencing. The GPS clock errors are estimated at 30-second intervals using International GPS Service (IGS) orbits and stations. The clock error estimates are then used in an absolute positioning algorithm to determine the coordinates without any other reference site. Static and kinematic GPS data at 1-second sampling rate were processed and compared with the known values and the corresponding DGPS solutions. For the static case, an IGS station was assumed as unknown and its coordinates were estimated. For the kinematic case, the aircraft survey observations were tested. The positions were compared with the corresponding DGPS solutions for each case. Since Selective Availability (SA) is now turned off, its effect on the clock estimation as well as on the position is compared and emphasized. [ABSTRACT FROM AUTHOR]

An algorithm for very accurate absolute positioning through Global Positioning System (GPS) satellite clock estimation has been developed. Using International GPS Service (IGS) precise orbits and measurements, GPS clock errors were estimated at 30-s intervals. Compared to values determined by the Jet Propulsion Laboratory, the agreement was at the level of about 0.1 ns (3 cm). The clock error estimates were then applied to an absolute positioning algorithm in both static and kinematic modes. For the static case, an IGS station was selected and the coordinates were estimated every 30 s. The estimated absolute position coordinates and the known values had a mean difference of up to 18 cm with standard deviation less than 2 cm. For the kinematic case, data obtained every second from a GPS buoy were tested and the result from the absolute positioning was compared to a differential GPS (DGPS) solution. The mean differences between the coordinates estimated by the two methods are less than 40 cm and the standard deviations are less than 25 cm. It was verified that this poorer standard deviation on 1-s position results is due to the clock error interpolation from 30-s estimates with Selective Availability (SA). After SA was turned off, higher-rate clock error estimates (such as 1 s) could be obtained by a simple interpolation with negligible corruption. Therefore, the proposed absolute positioning technique can be used to within a few centimeters' precision at any rate by estimating 30-s satellite clock errors and interpolating them. [ABSTRACT FROM AUTHOR]

In this paper, a dynamic positioning system using a rotating sonar and a differential encoder is proposed. The method is implemented by employing an indirect feedback Kalman filter. The state equation is written for encoder propagation and its error characteristic. A measurement equation describes a map-based measurement equation based on rotating sonar sensor data. In other words, sonar data compensates for the system and navigation errors of the differential encoder. The positioning system calculates the position and headings of a mobile robot. The real-time calculation is performed by a map-based measurement update utilizing wide-angle beam characteristics of the sonar sensor and the Kalman filter. In addition, an observability analysis for the positioning system is performed. Experimental results show that the proposed hybrid positioning system successfully provides accurate position and headings in real-time. The position and heading errors arc bounded within few centimeters and within few degrees, respectively. [ABSTRACT FROM AUTHOR]