RTK Positioning Research Articles

THE USE OF UNMANNED AIRCRAFT IN THE PRODUCTION PROCESS OF DRILLING AND BLASTING AT SURFACE MINES

Surface mines that have solid rocks in their geological structure require considerable dedication to the work processes of drilling and blasting. Drilling and blasting, as one of the first work processes in surface mines - quarries, affects all subsequent work processes (loading, transport and crushing) as a result. By improving the effects of drilling and blasting, KPI results are significantly improved on all subsequent work processes, as well as on the reduced impact of mining on the environment. The paper shows the use of UAVs (unmanned aerial vehicles) for the purpose of optimizing the results of drilling and blasting in the Anhovo quarry (carbonate mineral - R. Slovenia), whose entire annual production of 1.5×106 t goes to the cement industry (Alpacem cement d.d. Slovenia). The equipment used in the aforementioned quarry is a handheld Leica GNSS RTK device, a DJI Mavic 3E drone with RTK positioning, a Sandvik Ranger DX800i drilling rig with RTK positioning, as well as BlastMetrix software for processing data obtained from drone images and projecting minefields.

A Multimode Fusion-Based Aviation Communication System

This paper presents a new design for a multimode fusion communication system, aimed at tackling the complexities of modern aeronautical communication. The system integrates multiple communication technologies, such as ad hoc networking, 5G, BeiDou satellite, RTK positioning, and ADS-B broadcasting. This integration effectively solves the problem of increasing the size and weight of aviation communication equipment while also improving the efficiency and security of data communication. The study demonstrates that the implementation of this fusion communication system can lead to the development of more efficient and intelligent avionics equipment in the future, thereby offering robust technical support for flight safety.

Hidrografski premer međunarodnih plovnih puteva u Republici Srbiji

European inland waterways are a key element of the European transport network and are mostly used for freight traffic. The hydrographic surveying is the basis for the maintenance of inland waterways and the establishment of safe navigation. A part of the European waterway corridor E80 consists of the rivers Danube, Sava and Tisza, which part of their course also flows through the Republic of Serbia. On these sections of the mentioned rivers, the competent state institutions are conducting a continuous campaign of hydrographic measurements, which, among other things, includes GNSS RTK positioning and depth measurement with a single-beam ultrasonic echo sounder. In this paper, the characteristics of these sections of rivers, the current methodology of depth measuring and positioning during depth measuring will be shown in details.

An ionosphere-weighted calibration method with multi-station network corrections

Ionospheric delay is one of the most dominant error sources in GNSS fast relative positioning, especially for RTK positioning of medium and long baselines, which directly affects the ambiguity fixing successful rate and positioning accuracy. The strategy of combining ionospheric correction based on multi-reference station network with ionospheric weighted model is still one of the most effective methods for precise relative positioning. In this paper, a method of ionospheric weighted calibration model is presented. By using a large-scale reference station network at a certain period of time with ionospheric disturbance to obtain the prior ionospheric information required by the user, the GNSS precision relative positioning performance of the ionosphere-weighted calibration model in complex scenarios (the accuracy of prior ionospheric information will be reduced due to large-scale reference station network and ionospheric active scene) was systematically evaluated. The experimental results show that the ionosphere-weighted calibration (IWC) method can effectively reduce the influence of excessive ionospheric modeling residual on the positioning results, and significantly improve the fixed rate and positioning accuracy of RTK. Compared with the traditional ionosphere-fixed model based on virtual reference station (VRS) technology, the three-dimensional accuracy and fixed rate of the six rover stations are improved by 56% and 33.5% on average. Secondly, the prior ionospheric constraint intensity in IWC mode is controllable, which can effectively balance the relationship between initialization speed and positioning accuracy. On average, 94.3% of the time period of the six rover stations can complete the initialization and fixing within 10 epochs, which can basically meet the requirements of fast positioning. In addition, IWC model can ensure higher accuracy and better maintain fixed solution state after the ionospheric parameter convergence is completed. In the ionospheric disturbance stage, after a period of parameter convergence, high fixed rate and positioning accuracy can still be guaranteed.

An Improved Ambiguity Resolution Algorithm for Smartphone RTK Positioning.

Ambiguity resolution based on smartphone GNSS measurements can enable various potential applications that currently remain difficult due to ambiguity biases, especially under kinematic conditions. This study proposes an improved ambiguity resolution algorithm, which uses the search-and-shrink procedure coupled with the methods of the multi-epoch double-differenced residual test and the ambiguity majority tests for candidate vectors and ambiguities. By performing a static experiment with Xiaomi Mi 8, the AR efficiency of the proposed method is evaluated. Furthermore, a kinematic test with Google Pixel 5 verifies the effectiveness of the proposed method with improved positioning performance. In conclusion, centimeter-level smartphone positioning accuracy is achieved in both experiments, which is greatly improved compared with the float and traditional AR solutions.

The Superiority of Multi-GNSS L5/E5a/B2a Frequency Signals in Smartphones: Stochastic Modeling, Ambiguity Resolution, and RTK Positioning

The emerging Internet of Things (IoT) applications, such as intelligent transportation based on vehicular-lane accurate positioning, have a growing demand for precise and reliable positioning with Global Navigation Satellite Systems (GNSSs). It is desirable to use GNSS modules in smartphones to achieve highprecision positioning. The GNSS modules in some brands of smartphones thus far are able to track the new L5 signals of GPS and QZSS, E5a signals of Galileo and B2a signals of BeiDou-3. The L5/E5a/B2a signals have higher quality due to their signal structure, which provides an important potential for highprecision positioning in smartphones. In this paper, we will study the quality of L5/E5a/B2a signals, and their superiorities in integer ambiguity resolution (IAR) and precise positioning with respect to the L1/E1/B1 signals from GPS, QZSS, Galileo and Beidou-2/3 satellites. The signal quality is evaluated in terms of observation precision, multipath, double-differenced ambiguity fractions and ambiguity dilution of precision (ADOP). In addition, we propose a new weighting model that takes into account the variation range of carrier-to-noise density ratio (C/N0). The results indicate that the Beidou-3 B2a signal has comparable quality to L5/E5a signals of other systems, and all of them are better than the L1/E1/B1 signals. However, the ambiguity fractions of B2a signals diverge abruptly in some periods, resulting in the unsuccessful ambiguity fixing. The L5/E5a/B2a signals can generally obtain higher IAR fix-rate and positioning accuracies than the L1/E1/B1 signals. The new weighting model can capture the smartphone noise characteristics better than the traditional weighting model, thus improving the positioning accuracy.

RTK positioning based on the phase-only differential corrections

Multi-GNSS multi-frequency observations improve the accuracy, availability and reliability of the single-site RTK positioning but also simultaneously raise the communication bandwidth needed for the transmission of differential corrections. A RTK positioning algorithm is proposed that transmit the phase-only differential corrections to achieve the ambiguity-fixed RTK positioning, significantly reducing the communication bandwidth requirements. The essence of the presented method is that the code differential positioning solution implied in the conventional RTK positioning procedure can be replaced by the single point positioning solution of the rover receiver to realize RTK positioning. For typical application scenarios, the transmitted bits in a single epoch can be reduced by more than 25% when the corrections are sent with the RTCM protocol. The experiments by the GPS dual-frequency data over the 10 km and 180 km baselines shown that the performance of the presented RTK algorithm are comparable to that of the conventional RTK positioning, which verifies its feasibility and effectiveness.

Studies on Three-Dimensional (3D) Accuracy Optimization and Repeatability of UAV in Complex Pit-Rim Landforms As Assisted by Oblique Imaging and RTK Positioning.

Unmanned Aerial Vehicles (UAVs) are a novel technology for landform investigations, monitoring, as well as evolution analyses of long−term repeated observation. However, impacted by the sophisticated topographic environment, fluctuating terrain and incomplete field observations, significant differences have been found between 3D measurement accuracy and the Digital Surface Model (DSM). In this study, the DJI Phantom 4 RTK UAV was adopted to capture images of complex pit-rim landforms with significant elevation undulations. A repeated observation data acquisition scheme was proposed for a small amount of oblique-view imaging, while an ortho-view observation was conducted. Subsequently, the 3D scenes and DSMs were formed by employing Structure from Motion (SfM) and Multi-View Stereo (MVS) algorithms. Moreover, a comparison and 3D measurement accuracy analysis were conducted based on the internal and external precision by exploiting checkpoint and DSM of Difference (DoD) error analysis methods. As indicated by the results, the 3D scene plane for two imaging types could reach an accuracy of centimeters, whereas the elevation accuracy of the orthophoto dataset alone could only reach the decimeters (0.3049 m). However, only 6.30% of the total image number of oblique images was required to improve the elevation accuracy by one order of magnitude (0.0942 m). (2) An insignificant variation in internal accuracy was reported in oblique imaging-assisted datasets. In particular, SfM-MVS technology exhibited high reproducibility for repeated observations. By changing the number and position of oblique images, the external precision was able to increase effectively, the elevation error distribution was improved to become more concentrated and stable. Accordingly, a repeated observation method only including a few oblique images has been proposed and demonstrated in this study, which could optimize the elevation and improve the accuracy. The research results could provide practical and effective technology reference strategies for geomorphological surveys and repeated observation analyses in sophisticated mountain environments.

Spectral analysis of the phenological stages of Lupinus mutabilis through spectroradiometry and unmanned aerial vehicle imaging with different physical disinfection pretreatments of seeds

The economic and cultural importance of lupin has been identified in regions such as the alpine zone of Ecuador, where per capita consumption reaches 0.4 kg per month. However, fungal pathogens affect lupin cultivation, causing considerable crop losses. In this study, Lupinus mutabilis Sweet plants started from seeds were analysed using remote sensing techniques, and different physical disinfection pretreatments were applied. A total of 6 samplings were conducted according to the phenological stages of the crop. A spectroradiometer and an unmanned aerial vehicle were used to generate vegetation indices based on the red, near-infrared and red-edge bands. Using SfM photogrammetry and RTK positioning, the vegetation index values were extracted from the orthophotos and statistically analysed. All the vegetation indices exhibited significant differences between phenological stages, but the differences between pretreatments were not as clear. The best pretreatment was determined to be drying the seeds at ambient temperature for 45 minutes.

A Comparative Study of BDS Triple-Frequency Ambiguity Fixing Approaches for RTK Positioning.

Concerning the triple-frequency ambiguity resolution, in principle there are three different realizations. The first one is to fix all the ambiguities of the original frequencies together. However, it is also believed that fixing the combined integer ambiguities with longer wavelength, such as extra-wide-lane (EWL), wide-lane (WL), should be advantageous. Also, it is demonstrated that fixing sequentially EWL, WL and one type of original ambiguities provides better results, as the previously fixed ambiguities increase parameters’ precision for later fixings. In this paper, we undertake a comparative study of the three fixing approaches by means of experimental validation. In order to realize the three fixing approaches from the same information in terms of adjustment, we developed a processing strategy to provide fully consistent normal equations. We first generate the normal equation with the original undifferentiated carrier phase ambiguities, then map it into that with the combined and double-differenced ambiguities required by the individual approach for fixing. Four baselines of 258 m, 22 km, 47 km and 53 km are selected and processed in both static and kinematic mode using the three ambiguity-fixing approaches. Indicators including time of first fixed solution (TFFS), the correct fixing rate, positioning accuracy and RATIO are used to evaluate and investigate results. We also made a preliminary theoretical explanation of the results by looking into the decorrelation procedure of the ambiguity searching algorithm and the intermediate results. As conclusions, integrated searching of original ambiguities or combined ambiguities has almost the same fixing performance, whereas the sequential fixing of EWL, WL and B1 ambiguities overperforms the integrated searching. By the way, the third-frequency data can shorten the TFFS significantly but can hardly improve the positioning.

ANALYSIS OF GULLY EROSION IN A CATCHMENT AREA IN OLIVE GROVES USING UAS PHOTOGRAMMETRY TECHNIQUES

Abstract. An approach based on images captured by means of an Unmanned Aerial System (UAS) and Structure from Motion – Multi Video Stereo (SfM-MVS) photogrammetry is presented for the study of the gully erosion in a catchment area of about 16 ha. The study area is located in the province of Jaén (SW Spain) where the main land use is the olive groves. Three UAS flights have been made in April 2019, May 2019 and February 2020 with an average GSD of 2–3 cm. The image processing has been carried out using some field surveyed GNSS ground control points and the RTK positioning of the UAV with errors lower than 0.03 m and 0.04 m in XY and Z, respectively. Then DSMs and orthophotographs were obtained with a resolution of 0.10 m and 0.05 m, respectively, and DSM of differences (DoDs) were calculated, with an uncertainty of about ±0.15 m. Finally, the DoDs were analysed in the GIS, in order to calculate the height differences and volumes between the three flights. The analysis has showed the areas affected by the gully erosion processes that correspond mainly to ground descents due to significant channel erosion and mass movements at the steep sidewalls. Considering the balance between depletion and deposition processes, the average height differences is about −0.03 m and the volume is about −42 m3, that is the depletion predominates. The main changes have been detected in the second period (May 2019–February 2020), while in the first one (April 2019–May 2019) they are practically insignificant and limited to small areas.

Enhanced wide-area multi-GNSS RTK and rapid static positioning in the presence of ionospheric disturbances

Ionospheric disturbances are the phenomena which adversely affect the performance of precise positioning. This holds true even for multi-constellation relative positioning supported with network-derived ionospheric corrections. In such scenario the unfavorable effect is caused by a poor accuracy of corrections, which, in turn, is driven by the deterioration of the spatial interpolation process. The positioning becomes even more challenging in a wide-area scenario with baselines over 100 km. In this paper, we assess the methodology which aims at reliable and accurate wide-area RTK and rapid static positioning in the presence of severe ionospheric conditions. The approach takes advantage of multi-constellation network ionospheric corrections and an algorithm which allows the elimination of the temporal variations of the ionospheric delay. The experimental evaluation was performed on the basis of multi-station RTK and static positioning using GPS, BDS and Galileo data collected at high latitudes during the ionospheric storm on August 25–26, 2018. The results confirmed the deterioration of the accuracy of the network ionospheric corrections and consequently a decline in the positioning performance with routine models such as ionosphere-float and ionosphere-weighted. On the other hand, the results obtained with the application of the developed methodology demonstrated a very distinctive improvement in the ambiguity resolution domain and thus proved the advantage over benchmark models. In this case, the developed methodology allowed up to 20% enhancement of the ambiguity success rate with respect to benchmark strategies.

APPLICATION OF AN INERTIAL SYSTEM FOR COMPENSATION OF THE TILT OF A MARKER WITH ANTENNA IN GNSS RECEIVERS

The rapid development of GNSS, GNSS receivers of geodetic accuracy class, and inertial measurement units is offering a great opportunity to improve the applicability, productivity and user experience of high-precision RTK positioning. Benefiting from the tilt compensation technology, RTK positioning using a GNSS receiver can be used in difficult situations with increased speed and efficiency. In the article application of an inertial system for compensation of the marker tilt in GNSS receivers using Leica GS18 T as an example is considered, appropriate conclusions are made.

Integrity Monitoring for Horizontal RTK Positioning: New Weighting Model and Overbounding CDF in Open-Sky and Suburban Scenarios

Integrity monitoring is an essential task for ensuring the safety of positioning services. Under a selected probability of hazardous misleading information, the protection levels (PLs) are computed according to a considered threat model to bound the positioning errors. A warning message is sent to users when the PL exceeds a pre-set alert limit (AL). In the short-baseline real-time relative kinematic positioning, the spatially correlated errors, such as the the orbital errors and the atmospheric delays are significantly reduced. However, the remaining atmospheric residuals and the multipath that are not considered in the observation model could directly bias the positioning results. In this contribution, these biases are analysed with the focus put on the multipath effects in different measurement environments. A new observation weighting model considering both the elevation angle and the signal-to-noise ratios is developed and their impacts on the positional results are investigated. The coefficients of the proposed weighting model are determined for the open-sky and the suburban scenarios with the positional benefits maximised. Next, the overbounding excess-mass cumulative distribution functions (EMCs) are searched on the between-receiver level for the weighted phase and code observations in these two scenarios. Based on the mean and standard deviations of these EMCs, horizontal protection levels (HPLs) are computed for the ambiguity-fixed solutions of real experiments. The HPLs are compared with the horizontal positioning errors (HPEs) and the horizontal ALs (HALs). Using the sequential exclusion algorithm developed for the ambiguity resolution in this contribution, the full ambiguity resolution can be achieved in around 100% and 95% of the time for the open-sky and the suburban scenarios, respectively. The corresponding HPLs of the ambiguity-fixed solutions are at the sub-dm to dm-level for both scenarios, and all the valid ambiguity-fixed HPLs are below a HAL of 0.5 m. For the suburban scenario with more complicated multipath environments, the HPLs increase by considering extra biases to account for multipath under a certain elevation threshold. In complicated multipath environments, when this elevation threshold is set to 30 degrees, the availability of the ambiguity-fixed solutions could decrease to below 50% for applications requiring HAL as low as 0.1 m.

GNSS ambiguity resolution with ratio and fixed failure ratio tests for long baseline network RTK under ionospheric activity

To perform network RTK positioning, a user must receive and apply the information generated from a network. Corrections are generated for the user to consider the atmospheric delays (ionosphere and troposphere) between ther location and the network stations. In order to generate reliable corrections and send them to users, one must resolve the ambiguities in the processing step of the network stations. Ambiguities are the number of integer cycles of the carrier phase in the first data collection epoch and are introduced as parameters to be estimated in the processing. Thus, the ambiguity resolution process becomes a prerequisite for obtaining high accuracy in network RTK positioning. This process can be divided into two steps: estimation and validation. The estimation step aims to obtain the integer values of ambiguities and in the validation step it is inferred if the estimated integer value may or may not be accepted. In this work, the LAMBDA (Least squares AMBiguity Decorrelation Adjustment) method was used to obtain the integer ambiguity estimate and for the validation the Ratio and FF-RT (Fixed Failure Ratio Test) tests were used. The objective of this work was to investigate the performance of the ambiguities validation tests for long baselines. The results showed that the FF-RT test presented the highest fixed ambiguity percentages when compared to the Ratio test in all analyzed periods. Thus, for long baselines positioning, in periods of either weak or strong ionospheric activity, the use of the FF-RT test will cause a greater number of fixed ambiguities to be used in the process of generating the corrections for the user.

Research on fast fixing algorithm of PPP-RTK ambiguity

The PPP-RTK technology, which combines the advantages of network RTK (NRTK) and precision point positioning (PPP) technology, has become a hotspot of current precision positioning research. This paper proposes a solution to quickly fix the ambiguity, Which can improves the reliability of ambiguity estimation. In the experiment, the measured data of the IGS station are used to perform PPP-RTK positioning solution, Statistics show that:When using this algorithm to locate the static data, it takes about 20 minutes for the data convergence time to reach the centimeter level. The accuracy of the positioning results has reached the centimeter level, The positioning accuracy in the plane position direction is better than 3 cm, and the positioning accuracy in the elevation direction is better than 5 cm.

A Triple Checked Partial Ambiguity Resolution for GPS/BDS RTK Positioning.

Reliable and accurate carrier phase ambiguity resolution is the key to high-precision Global Navigation Satellite System (GNSS) positioning and application. With the fast development of modern GNSS, the increased number of satellites and ambiguities makes it hard to fix all ambiguities completely and correctly. The partial ambiguity fixing technique, which selects a suitable subset of high-dimensional ambiguities to fix, is beneficial for improving the fixed success rate and reliability of ambiguity resolution. In this contribution, the bootstrapping success rate, bounded fixed-failure ratio test, and the new defined baseline precision defect are used for the selection of the ambiguity subset. Then a model and data dual-driven partial ambiguity resolution method is proposed with the above three checks imposed on it, which is named the Triple Checked Partial Ambiguity Resolution (TC-PAR). The comprehensive performance of TC-PAR compared to the full-fixed LAMBDA method is also analyzed based on several criteria including the fixed rate, the fixed success rate and correct fixed rate of ambiguity as well as the precision defect and RMS of the baseline solution. The results show that TC-PAR could significantly improve the fixed success rate of ambiguity, and it has a comparable baseline precision to the LAMBDA method, both of which are at centimeter level after ambiguities are fixed.

Combined BeiDou-2 and BeiDou-3 instantaneous RTK positioning: stochastic modeling and positioning performance assessment

ABSTRACT The global BeiDou navigation satellite system (BDS-3) has been in operation recently and many related applications have been already compatible with BDS-3 satellites. Most applications still use the empirical stochastic models for combined regional BeiDou navigation satellite system (BDS-2) and BDS-3 positioning. However, BDS-3 has different satellite design, and the empirical stochastic models may not describe the observation precisions and the correlation characteristics of BDS-3 signals well and finally degrade the positioning performance. Hence, in this contribution, the variance-covariance component estimation is applied to calculate the precisions of observations and their spatiotemporal correlations as well as the cross-correlations for BDS-2 and BDS-3 multi-frequency signals. With the retrieved stochastic model, the performance of integer ambiguity resolution and positioning are then numerically demonstrated on short baseline. The results show that the observation precisions are in general elevation-dependent for both BDS-2 and BDS-3 except for BDS-2 geostationary earth orbit (GEO) satellites. For both BDS-2 and BDS-3, the spatial correlations are adequately small to be ignored in practical data processing. For the receivers we used, the cross-correlations are found significantly amongst the BDS-2 multi-frequency phase signals. Moreover, the temporal correlations differ between different frequencies and observations. The combined BDS-2 and BDS-3 can improve the ambiguity resolution success rate and positioning accuracy.

Assessment of the Single Frequency Low Cost GPS RTK Positioning

The Global Navigation Satellite System (GNSS), nowadays, is to be an important tool for determining positions and times on the real-time and post-processing applications. This study aims to assess the performance of the single frequency L1-GPS using low cost receivers. The performance will be evaluated by comparing with the geodetic L1+L2 GPS receiver to positioning performance. The low cost receivers used were Ublox NEO-M8T and Allystar HD9100. While, the dual frequency GPS TOPCON was used as reference receiver. The results show, RTK mode can improve the accuracy compare with single positioning up to centimetres. In this experiment, the Allystar HD9100 gives a better result than Ublox Neo M8T. However, the result discrepancies may be caused by the simple antenna splitter.

ОПЫТ ПРАКТИЧЕСКОГО ПРИМЕНЕНИЯ МЕСТНОЙ АВТОМАТИЗИРОВАННОЙ ГЕОДЕЗИЧЕСКОЙ СЕТИ НА БАЗЕ ОТЕЧЕСТВЕННОЙ ГНСС-АППАРАТУРЫ

In article the local automatized geodetic network (MAGS) that provides RTK and post-processed relative positioning for geotechnical monitoring. The net based on using of GNSS receiv-ers and software which made in Russia. The results of practical tests are showed.