Real-time Kinematic Measurements Research Articles

Decimeter-Level Accuracy for Smartphone Real-Time Kinematic Positioning Implementing a Robust Kalman Filter Approach and Inertial Navigation System Infusion in Complex Urban Environments.

New smartphones provide real-time access to GNSS pseudorange, Doppler, or carrier-phase measurement data at 1 Hz. Simultaneously, they can receive corrections broadcast by GNSS reference stations to perform real-time kinematic (RTK) positioning. This study aims at the real-time positioning capabilities of smartphones using raw GNSS measurements as a conventional method and proposes an improvement to the positioning through the integration of Inertial Navigation System (INS) measurements. A U-Blox GNSS receiver, model ZED-F9R, was used as a benchmark for comparison. We propose an enhanced ambiguity resolution algorithm that integrates the traditional LAMBDA method with an adaptive thresholding mechanism based on real-time quality metrics. The RTK/INS fusion method integrates RTK and INS measurements using an extended Kalman filter (EKF), where the state vector x includes the position, velocity, orientation, and their respective biases. The innovation here is the inclusion of a real-time weighting scheme that adjusts the contribution of the RTK and INS measurements based on their current estimated accuracy. Also, we use the tightly coupled (TC) RTK/INS fusion framework. By leveraging INS data, the system can maintain accurate positioning even when the GNSS data are unreliable, allowing for the detection and exclusion of abnormal GNSS measurements. However, in complex urban areas such as Qazvin City in Iran, the fusion method achieved positioning accuracies of approximately 0.380 m and 0.415 m for the Xiaomi Mi 8 and Samsung Galaxy S21 Ultra smartphones, respectively. The subsequent detailed analysis across different urban streets emphasized the significance of choosing the right positioning method based on the environmental conditions. In most cases, RTK positioning outperformed Single-Point Positioning (SPP), offering decimeter-level precision, while the fusion method bridged the gap between the two, showcasing improved stability accuracy. The comparative performance between the Samsung Galaxy S21 Ultra and Xiaomi Mi 8 revealed minor differences, likely attributed to variations in the hardware design and software algorithms. The fusion method emerged as a valuable alternative when the RTK signals were unavailable or impractical. This demonstrates the potential of integrating RTK and INS measurements for enhanced real-time smartphone positioning, particularly in challenging urban environments.

Accuracy Assessment of UAV Photogrammetry System with RTK Measurements for Direct Georeferencing

Abstract. The direct georeferencing accuracy of unmanned aerial vehicle (UAV) images with real-time kinematic (RTK) measurements is a concerned topic in the community of photogrammetry. This study assesses the capabilities of a multi-rotor platform equipped with RTK technology, specifically a DJI Phantom 4 RTK UAV, for robust direct georeferencing. The UAV surveyed a square and a building at Wuhan University to assess the accuracy and spatial consistency of direct georeferencing in close-range photography. We tested checkpoint errors under various ground control points (GCPs) configurations. The results show that without GCP, an analysis of 71 spatially distributed checkpoints produced a root mean square error (RMSE) of 5.58 cm in the Z direction. This finding indicates that RTK-equipped UAVs can achieve acceptable error margins even without using GCPs, thereby fulfilling the precision requirements for large-scale mapping.

Analysis of differences in accuracy of positioning tied to various CORS networks in Poland: Case study

Abstract Network Real Time Kinematic (NRTK) measurements are currently the most popular surveying method in geodesy. In most countries, there are networks of Continuously Operating Reference Stations (CORS), which form the core of the terrestrial infrastructure that allows for NRTK measurements. In many countries, including Poland, several CORS networks operate in parallel and independently. The paper presents the characteristics of the CORS network in Poland. The results of several day NRTK and Real Time Kinematic (RTK) test measurements performed tied to five CORS networks operating in Poland: ASG-EUPOS, NadowskiNET, SmartNet, TPINETpro, VRSNet.pl, were subjected to a comparative analysis. VRS, FKP, MAC and POJ streams were used in the test measurements. The research mainly concerned the possibility of the occurrence of systematic errors when NRTK and RTK measurements were tied to different CORS networks for the survey of the same points. Conclusions from the comparative analysis of the accuracy and precision of the NRTK and RTK measurement results for each coordinate were also included.

Spatio-Temporal Analysis of Ground Movement Using Unmanned Aerial Vehicle Photogrammetry in Gampong Lamkleng, Aceh Besar

Ground movement is one of the most frequent disasters causing major damages in Indonesia. Unmanned Aerial Vehicle (UAV) has been widely used as a rapid observation method to obtain detailed characterization of ground movement. Often, active landslide area is difficult to access. This hinders close monitoring and observations of the ground movement. This study aims to demonstrate the use of UAV as tools for monitoring and observations on active ground movement area and to validate the results. For this purpose, the study was conducted at Gampong Lamkleng, Aceh Besar-Indonesia using spatio-temporal analysis by UAV photogrammetry. The UAV was chosen because it is easy to use, practical, and safe for landslide area that are relatively small and difficult to reach. Aerial photographs were processed using the Agisoft Metashape software in modeling and analyzed using Quantum GIS (QGIS) and ArcGis. The observation results show that the largest ground movement occurred in January 20 to 23, 2021 which was related to precipitation rates measured at a nearby rainfall station. The movement volume was 1,411.063 m3 and a rate of ground movement reaching 0.69 m/day due to heavy rain. The estimated value of losses is IDR 1,055,854,000. The UAV images analysis were compared to actual ground elevation measured using Real-Time Kinematic (RTK). The validation show that the accuracy based on comparison between photogrammetric and RTK measurement was at agreeable rate (99%). Otherwise, the accuracy performed on 19 check point using Root Mean Square Error analysis found that the accuracy was still very low. The low RMSE value is due to the georeferencing process using the Ground Control Point not being carried out.

Toward the Future Generation of Railway Localization Exploiting RTK and GNSS

Smart sensors have become pervasive in railway transportation applications, particularly in Europe where digital technologies are increasingly being applied to the railway signalling field. In the future, safety-critical track-side train detection equipment, such as track circuits and axle counters, will be eliminated in favor of an accurate position estimate supplied by the train. However, the best approach to calculate an accurate position estimate remains an open research question, especially due to the high availability and reliability required. This paper describes two static experiments performed with a GNSS module, which demonstrate that the real-world accuracy achievable with GNSS and Real Time Kinematic (RTK) alone is not sufficient for safety-critical applications, meaning further complementary sensors are required. Furthermore, a custom sensor node containing a GNSS module with RTK and an Inertial Measurement Unit (IMU) has been used to acquire several data sets from an operating passenger train during dynamic tests on a railway line between Formigine and Modena, in Emilia-Romagna, Italy. These labeled GNSS and IMU data have been made freely available to the scientific community. The positioning accuracy of the GNSS and RTK measurements is evaluated, providing an in-depth study of the localization error and satellite coverage on the entire route. We demonstrate, with experimental evaluation, that centimeter accuracy (1.9 ± 0.8 cm) is achievable under favorable static conditions, while accuracy can deteriorate to 8m with RTK in urban scenarios with many reflections and poor sky view, worse than with GNSS alone. Under controlled conditions we show that shielding the GNSS receiver without RTK with a grounded metal plate causes a reduction in accuracy from 0.80 ± 0.04m to 3.70 ± 0.55m in the least and most shielded case respectively. Our dynamic tests on a train show that although at least meter-level accuracy (1.08 ± 1.30 m) is achievable with GNSS and RTK alone under dynamic conditions, a sensor fusion approach is necessary to accurately localize trains when GNSS conditions are poor or GNSS is unavailable.

Comparative analysis of the performance of Multi-GNSS RTK: A case study in Turkey

The Real Time Kinematic (RTK) method is widely used in the land surveying. Whereas RTK method has the advantage of practical use, positioning accuracy depends mostly on the baseline length due to the atmospheric errors. In general, RTK measurements are made by using GPS and GLONASS satellite systems. For this reason, the positioning performance of the technique is adversely affected under restricted satellite geometry conditions such as urban canyons. At present, most receivers on the market have the ability to track signals of Galileo and BeiDou satellites. Therefore, in this study, the positioning performance of RTK with different satellite combinations (GPS-only, GPS+GLONASS, GPS+GLONASS+GALILEO+BeiDou) was examined with a comparative approach. A field test was carried out considering approximately 20, 40, 60, and 80 km length of baselines. Three different cut off elevation angles – namely, 10°, 20°, and 30° – were chosen for the field test. The results were investigated in terms of accuracy and precision. Also, the ground truth coordinates of the rovers were obtained by post-processing relative method using GAMIT/GLOBK software. The results showed that multi-GNSS combinations provided better repeatability at the 10° cut off angle option. The accuracy of GPS-only solutions varied between 0.63/2.17 cm and 2.40/4.94 cm for horizontal and vertical components, respectively. However, the multi-GNSS combinations did not have a remarkable superiority in terms of position accuracy even at high satellite cut off angle (30°) compared to the GPS-only RTK.

Antenna Array-Aided Real-Time Kinematic Using Moving Base Stations

A global navigation satellite systems (GNSS) real-time kinematic (RTK) using multiple base stations is referred as an antenna array-aided RTK. This positioning method more reliably resolves carrier phase integer ambiguities by processing additional measurements provided from multiple GNSS reference stations whose antenna locations are accurately surveyed. In this study, a conventional antenna array-aided RTK is extended to improve RTK performance with multiple moving base stations. Because accurately surveyed antenna coordinates are not available, we propose an antenna array-aided Kalman filter approach to first check the sanity of the fixed integer ambiguities and baselines estimated by moving reference stations and use them as a-priori information in RTK measurement formulations. Our flight test results with three unmanned aerial vehicles confirmed that the proposed Kalman filter formulation outperformed the conventional RTK and a priori antenna array-aided RTK approaches in the aspects of positioning accuracy, time to first fix, and success probability of integer ambiguity fixes.

Individual Tree Detection and Qualitative Inventory of a Eucalyptus sp. Stand Using UAV Photogrammetry Data

Digital aerial photogrammetry (DAP) data acquired by unmanned aerial vehicles (UAV) have been increasingly used for forest inventory and monitoring. In this study, we evaluated the potential of UAV photogrammetry data to detect individual trees, estimate their heights (ht), and monitor the initial silvicultural quality of a 1.5-year-old Eucalyptus sp. stand in northeastern Brazil. DAP estimates were compared with accurate tree locations obtained with real time kinematic (RTK) positioning and direct height measurements obtained in the field. In addition, we assessed the quality of a DAP-UAV digital terrain model (DTM) derived using an alternative ground classification approach and investigated its performance in the retrieval of individual tree attributes. The DTM built for the stand presented an RMSE of 0.099 m relative to the RTK measurements, showing no bias. The normalized 3D point cloud enabled the identification of over 95% of the stand trees and the estimation of their heights with an RMSE of 0.36 m (11%). However, ht was systematically underestimated, with a bias of 0.22 m (6.7%). A linear regression model, was fitted to estimate tree height from a maximum height metric derived from the point cloud reduced the RMSE by 20%. An assessment of uniformity indices calculated from both field and DAP heights showed no statistical difference. The results suggest that products derived from DAP-UAV may be used to generate accurate DTMs in young Eucalyptus sp. stands, detect individual trees, estimate ht, and determine stand uniformity with the same level of accuracy obtained in traditional forest inventories.

Feasibility of Using Low-Cost Dual-Frequency GNSS Receivers for Land Surveying.

Global Navigation Satellite Systems (GNSS) have revolutionized land surveying, by determining position coordinates with centimeter-level accuracy in real-time or up to sub-millimeter accuracy in post-processing solutions. Although low-cost single-frequency receivers do not meet the accuracy requirements of many surveying applications, multi-frequency hardware is expected to overcome the major issues. Therefore, this paper is aimed at investigating the performance of a u-blox ZED-F9P receiver, connected to a u-blox ANN-MB-00-00 antenna, during multiple field experiments. Satisfactory signal acquisition was noticed but it resulted as >7 dB Hz weaker than with a geodetic-grade receiver, especially for low-elevation mask signals. In the static mode, the ambiguity fixing rate reaches 80%, and a horizontal accuracy of few centimeters was achieved during an hour-long session. Similar accuracy was achieved with the Precise Point Positioning (PPP) if a session is extended to at least 2.5 h. Real-Time Kinematic (RTK) and Network RTK measurements achieved a horizontal accuracy better than 5 cm and a sub-decimeter vertical accuracy. If a base station constituted by a low-cost receiver is used, the horizontal accuracy degrades by a factor of two and such a setup may lead to an inaccurate height determination under dynamic surveying conditions, e.g., rotating antenna of the mobile receiver.

Precision performance evaluation of RTK and RTN solutions: a case study

ABSTRACT Throughout the past few decades, advancements in global navigation satellite systems (GNSS), such as the Global Positioning System (GPS), have resulted in real-time planimetric accuracy at the centimetre level, whether achieved using Real-Time Kinematic (RTK) or Real-Time Network (RTN) approaches. This study examines and characterizes the performance of RTK and RTN solutions at three test sites in Los Angeles County, California, in the United States of America. The solutions were characterized to examine the dispersion of vertical measurements in the context of different environments. The results from this study suggest that both methods have advantages and drawbacks; in particular, the data showed that the distribution and density of the network stations, cellular network coverage and environmental dynamics have significant impacts on RTN vertical precision, where the vertical precision for the RTN measurements were observed to be 2–4 times lower in comparison to the RTK measurements.

GNSS RTK Performance Improvements using Galileo Satellite Signal

Abstract Two factors of the existing GNSS Real-Time Kinematic (RTK) positioning are as follows: distance-dependence and unreliable ambiguity resolution under bad observation conditions in cities or forests. Use of multi-frequency GNSS signals and systems could possibly redefine RTK services in LatPos, regionally and globally, and more redundant measurements from multiple satellite systems, such as NAVSTAR, Galileo, Glonass and BeiDou, can improve the performance of RTK measurement results in terms of accuracy, availability, reliability and time to fix. The benefits of multiple systems of GNSS services are as follows: 1) savings in the reference station infrastructure costs, and 2) improvement on RTK preciseness and reliability for the professional users. The paper aims at studying how the RTK system, using multiple satellite constellations, performs, adding Galileo signal measurements. Galileo measurements are observed using a field receiver and corrections received from LatPos base station network. Numerical analysis is performed using real-time corrections in field receivers, and results from collected RINEX data are compared by various computing schemes, such as L1/L2 and wide lane signals, NAVSTAR and NAVSTAR with Galileo measurements. The results have preliminary demonstrated the significant improvement using both GNSS satellite signals. Further improvements on the LatPos system have been introduced and the planned improvements shown.

Kinematic Studies in the Field of Accuracy and Position Determination of Aircrafts Using the PPP Technique by the GPS System

This article discusses the results of the measurements of position accuracy in 3D space for a UAV object using real-time kinematic measurements of the GPS system. The aim of the research presented in the work was to determine all three components (x, y, z) describing the location of the UAV object during the flight and making comparative characteristics using the PPS navigation service. Comparison of the differences between the two methods showed that the obtained results are characterized by a 95% of certainty. The results obtained in this experiment showed the accuracy of height measurement using the PPS GNSS system at a level of 10-80 centimeters. The results of this study also indicate that kinematic measurements can be very useful in the work of the air traffic controller and engineers of other specialties involved in position determination using satellite techniques. The article also presents a mathematical model defining the process of determining the position of a UAV object during the flight, taking into account kinematic measurements. In the final part of the work, practical conclusions were presented based on the analysis and selected simulation tests.

A multi-scale comparison of elevation measurement methods in northeastern tidal marshes of the United States

Coastal ecosystems are at risk across the globe due to combined effects of sea-level rise and human development. This threat is prevalent in the northeastern USA, where sea levels increase 2-6 mm annually. Much of this coastline is buffered by tidal marsh, directly linking monitoring of this ecosystem to effective coastal management into the future. We estimated local and regional elevations of tidal marshes from Maine to Virginia using real-time kinematic (RTK) technology, unmanned aircraft system (UAS) technology, and regional datasets from the National Elevation Dataset (NED) to evaluate elevation monitoring methods for coastal marshes. Locally we found that RTK-sourced elevation measurements are predicted well using the 1/9 arc-second NED layer, however UAS-derived DSMs did not predict RTK values well. Regionally we found the 1/9 arc-second NED explained 90% of the variation in RTK measurements, and this relationship was strongest in high marsh and terrestrial border across spatial scales. Additionally, we found that elevation increases from south to north in the majority of marsh cover types, indicating that continent-scale mechanisms may determine elevation relative to mean sea level. We suggest further work using UAS-sourced Digital Terrain Models and the NED as an economical substitute for RTK in higher-elevation cover types.

Statistical analysis of accuracy and precision of GNSS receivers used in network RTK

It is important to make accurate and precise measurements in surveying applications. The concepts of accuracy and precision are not synonymous, even though they are commonly used in place of each other. Nowadays, real-time kinematic (RTK) method is widely used at surveying. As the RTK method can be done depending on a reference station, in countries which establish Continuously Operating Reference Stations (CORS) Network, method known as Network-RTK (N-RTK) can be done depending on the CORS Network. Continuously Operating Reference Stations-Turkey Network (CORS-TR), which consists of 146 reference stations that allow positioning both real time and post-process, was established in 2009. In this study, accuracy and precision of Global Navigation Satellite Systems (GNSS) receivers are tried to determine depending on different correction techniques. For this purpose, 12-h GNSS observations were performed at SLCK-Turkish National Fundamental GPS Network (SLCK-TNFGN) point. The observations were adjusted based on CORS-TR. N-RTK measurements were performed with different GNSS receivers, and accuracies of the receivers were investigated. In order to determine precisions of the receivers, means of RTK measurements were calculated and precisions of the receivers were determined. As a result of investigation, it is seen that accuracy and precision of receivers at 2D positioning and height vary depending on correction technique.

Evaluation of the accuracy of lidar data acquired using a UAS for levee monitoring: preliminary results

ABSTRACTThis article presents the preliminary results of the possibilities for using an unmanned aerial system (UAS) for three-dimensional (3D) data collection for levees. The UAS is equipped with an ultra-light laser scanner and digital camera that acquires data with stereoscopic coverage. Sensors have been mounted on the multi-rotor. Using such a platform allows obtaining the 3D data necessary for circular surveying works with regard to levee monitoring for the prevention of flooding. Such a platform can offer an alternative to typical direct surveying measurements performed during the monitoring of such objects. It can detect changes in the multi-temporal analysis and evaluate the condition of levees ought to continuity of surface measurement and huge density of data up to dozens points per square metre. Lidar data and images of the levees were provided for several hundred metres of test area. In presented research, several flying missions were carried out which provided data that allowed for an analysis presenting the influence of the technique for initial georeferencing, altitude over the terrain, scanning lines’ length, overlap between scanning lines on the accuracy of relative orientation and absolute accuracy of the digital terrain model (DTM) that was created. The Iterative Closest Point algorithm and measurements of the natural and signalized control points were used to georeference and validate the lidar data obtained from the UAS. As reference data, Global Navigation Satellite System in real-time kinematic measurements was used to evaluate the absolute accuracy of the DTMs generated for the test area. The images captured from the UAS were a different data source which was checked to evaluate their usefulness in the considered application. A final accuracy close to 0.1 m was obtained for the generation of the DTM. The research proved the potential of this new kind of lidar data that can be acquired using ultra-light laser scanners.

Evidence – The intraoral palpability of the lateral pterygoid muscle – A prospective study

The intraoral palpability of the inferior caput of the lateral pterygoid muscle has been a matter of ambiguity because of its topography. Thus, none of the recently published studies has provided reliable proof of the possibility of digital intraoral palpation, although palpation of the muscle is part of most of the examination catalogs for clinical functional analysis and functional therapy.Digital muscle palpation was performed intraorally on five preparations after exposure of the infratemporal fossa and visualization of the lateral pterygoid muscle. Direct digital palpation of the lateral pterygoid muscle was seen in all five cases. The successful palpation was carried out and approved during laterotrusion to the examined side (relaxation). While opening and closing the mouth (contraction) the muscle is palpable. In real-time kinematic measurements (MRI) an impression of the lateral caput of the left lateral pterygoid muscle of a 30-year-old control male person was found up to 6mm. Electromyographic detection by direct signal conduction with concomitant palpation is possible. The injection electrode tested in situ in the muscle was felt transorally with the palpating finger.The intraoral palpability of the inferior caput of the lateral pterygoid muscle is verified. The basic requirement for successfully palpating the lateral pterygoid muscle is the exact knowledge of muscle topography and the intraoral palpation pathway. After documented palpation of the muscle belly in cadaverous preparations, MRI and EMG also visualized palpation of the lateral pterygoid muscle in vivo. The palpation technique seems to be essential and basically feasible.

Alternative Solutions for RTK-GPS Applications in Building and Road Constructions

Currently, Global Positioning System (GPS) techniques are becoming a much larger part of the surveying industry. Many companies are now using GPS in their everyday work activities. The Real Time Kinematic (RTK) positioning is an integral part of topographic surveys, road surveying, constructions and most civil engineering applications. Normally, RTK can be used to collect the positioning data successfully and quickly. The civil and construction projects are designed in ground distances while RTK measurements are done in grid coordinate system, in which the distances between points are different from ground. The RTK measurements should be converted to ground for compatibility with the designed. In this paper, the accuracy of three alternatives for converting RTK measurements to ground was studied. These alternatives are, using scale factor, using two ground reference points and using Low Distortion Projection (LDP) surface. For the accuracy investigation purpose, a traverse of 14 points elongated for a distance of about 1400 m was constructed. Its coordinates were measured using total station, then the misclosure error was computed and the coordinates were adjusted. The traverse points coordinates were measured again using RTK_GPS considering one of them as base point. The three studied alternatives were applied and the results were compared. The results show that the accuracy of the three alternatives is ranging from 2.1 to 2.9 cm in the relative position of points to the base point. For absolute position accuracy, the two ground reference points alternative is the most accurate alternative with an average error of 3.8 cm while the other two alternatives are almost the same with an average error of 12.3 cm.

Determination of coastal border line: an integrated approach for a part of Antalya coast (Turkey)

Sustainable development in coastal areas requires mapping of geological and geomorphological features of the area and precise determination of coastal border line. Such a study was carried out in the city of Antalya, which is undergoing intense infrastructural development in order to accommodate touristic activities. In the field, high water level, which is determined from moist-dry sand border and current berm crest, was taken as the indicator for shoreline, while vegetation line and topographic rises were taken as indicators of coastal border line. The geographic coordinates of all of the features were determined using differential Global Positioning System with application of “real-time kinematic measurement” technique. Quickbird satellite images of 2002 and 2009 were used in order to observe natural state of the coastal area before the constructions, to complete geomorphological map, and to confirm the coastal border line determined in the field. In addition, the natural vegetation line before the infrastructural development was determined using normalized difference vegetation index approach. Using grain size parameters for identification of coastal border line, high and low water levels were tested. The results showed that from low water level to coastal border line, D 50 (median grain size) and coefficient of uniformity decrease while coefficient of curvature increases systematically. This study showed that use of only one approach to determine coastal border line is insufficient, and an integrated methodology is required.

Gps precise point positioning with kinematic data

Nowadays most of the users needing geodetic accuracy use the Global Positioning System (GPS) with static measurements or with RTK (Real Time Kinematic) measurements. Few seconds are available to measure a detail point, therefore only the RTK method can satisfy the expectations. In this case (called observation space) the users require corrections from a base station. These corrections are available from the user’s own base station or they can be downloaded from the Internet if active permanent network is available in the area. There are many locations where kinematic data is recorded and have to be processed without owned base stations or without active permanent networks. For example, LEO (Low-Earth Orbit) satellite’s GPS receivers, ocean surface monitoring with GPS buoys or archaeological exploration in countries without geodetic base. This paper investigates the possibility of PPP (Precise Point Positioning) method processing kinematic data. It is known that the accuracy of this technique is enough in ...

Performance of RTK Positioning in Forest Conditions: Case Study

This paper presents the performance of the real-time kinematic (RTK) technique in very severe conditions. The measurements were conducted in forest conditions during two different experiments. Two Global Positioning System receivers were used: an Ashtech Z-Surveyor and a Z-Xtreme. Radiomodems were used for transmitting RTK corrections from a reference station to a rover. The RTK measurements were performed during quite good satellite configuration. The use of RTK technology, based on the Ashtech Z-Xtreme receiver as a rover in forest terrain, allowed centimeter accuracy to be obtained. However, practical experiments showed that there is a need for redundant independent RTK solutions based on repeated independent ambiguity reinitializations. Although gross errors might occur, the RTK technique can be very helpful technology for centimeter positioning in woodland areas.