Precise Positioning Results Research Articles

Relationship between GIX, SIDX, and ROTI ionospheric indices and GNSS precise positioning results under geomagnetic storms

Ionospheric indices give information about ionospheric perturbations, which may cause absorption, diffraction, refraction, and scattering of radio signals, including those from global navigation satellite systems (GNSS). Therefore, there may be a relationship between index values and GNSS positioning results. A thorough understanding of ionospheric indices and their relationship to positioning results can help monitor and forecast the reliability and accuracy of GNSS positioning and support the precision and safety of life applications. In this study, we present the relationship between three indices: Gradient Ionosphere indeX (GIX), Sudden Ionospheric Disturbance indeX (SIDX), and Rate of Total electron content Index (ROTI) in relation to precise positioning results. We used two approaches: precise point positioning (PPP) and relative positioning for long baselines. We focus on GNSS stations located in Europe for two selected geomagnetic storms: March 17, 2015, and May 22, 2015. Our results show that in the case of PPP, positioning degradation occurred mainly at high latitudes and was mostly caused by rapid small-scale changes in ionospheric electron content represented by SIDX and ROTI. We also showed a significant correlation between cycle slips of GNSS signals and ROTI (0.88). The most significant degradations for relative positioning for low and medium latitudes were associated with large spatial gradients reflected by the GIX.

Generalization of PhaseNet in Shandong and its application to the Changqing M4.1 earthquake sequence

Waveforms of seismic events, extracted from January 2019 to December 2021 were used to construct a test dataset to investigate the generalizability of PhaseNet in the Shandong region. The results show that errors in the picking of seismic phases (P- and S-waves) had a broadly normal distribution, mainly concentrated in the ranges of −0.4–0.3 s and −0.4–0.8 s, respectively. These results were compared with those published in the original PhaseNet article and were found to be approximately 0.2–0.4 s larger. PhaseNet had a strong generalizability for P- and S-wave picking for epicentral distances of less than 120 km and 110 km, respectively. However, the phase recall rate decreased rapidly when these distances were exceeded. Furthermore, the generalizability of PhaseNet was essentially unaffected by magnitude. The M4.1 earthquake sequence in Changqing, Shandong province, China, that occurred on February 18, 2020, was adopted as a case study. PhaseNet detected more than twice the number of earthquakes in the manually obtained catalog. This further verified that PhaseNet has strong generalizability in the Shandong region, and a high-precision earthquake catalog was constructed. According to these precise positioning results, two earthquake sequences occurred in the study area, and the southern cluster may have been triggered by the northern cluster. The focal mechanism solution, regional stress field, and the location results of the northern earthquake sequence indicated that the seismic force of the earthquake was consistent with the regional stress field.

ACHIEVING CENTIMETERS-LEVEL GPS POSITIONING ACCURACY USING A SMARTPHONE FOR MAPPING APPLICATIONS

Abstract. Nowadays, GNSS chips inside modern smartphones deliver high-quality code and carrier phase measurements which may be applied in various mobile applications, especially in mapping applications. In this situation, the usefulness of a professional geodetic receiver is commonly met to reach centimeters and sub-centimeter accuracies. To obtain such precise positioning results, carrier-phase measurements should be used. Therefore, we decided to check the Huawei P 30 Pro smartphone GNSS-based positioning system which may be an excellent tool to fast and accurately measure the points or details which may need to be precisely mapped with accuracies within centimeters. According to the tested smartphones' postprocessing RTKLib 2.4.3 software results, we could fix all L1 ambiguities based on GPS-only satellite constellation. After the comparison to reference fixed point position, for all 1-hour static session results, positioning errors were at centimeters level of accuracy (1-5cm). For fast static surveying mode, the best results were obtained for 30-minute sessions, where average accuracy was also at centimeters level (close to the level of a professional geodetic receiver).

Mobile Feature Enhanced High-Accuracy Positioning Based on Carrier Phase and Bayesian Estimation

The mobile feature and the moving positions are important for mobile communications and Internet of Things. Inspired by the potentially excellent precision of carrier phase positioning, this article proposes a mobile feature enhanced high-accuracy positioning algorithm based on the carrier phase and Bayesian estimation. The mobile feature is first estimated using time-differential carrier phase measurements. By combining the estimated position changes with instant ranging and carrier phase measurements, the factorized posterior probability of positioning is established based on the Bayes theorem. In turn, a factor graph-based positioning method is proposed to obtain precise positioning results. The numerical simulation results show that the proposed algorithm can achieve centimeter-level accuracy, and the positioning error can approach the Cramer–Rao lower bound.

Online Pantograph-Catenary Contact Point Detection in Complicated Background Based on Multiple Strategies

Monitoring train operation status is one of the most important tasks for ensuring rail operation safety. Pantograph and catenary (PAC) are collecting systems of the electric current from traction power supply system, and the stability of the contact between pantograph and catenary guarantees the stable power. However, most existing contact point (CPT) detection methods are always difficult to achieve precise positioning results, especially in complicated background. This article proposes a novel fast and accurate contact point detection method based on multiple strategies, which combine three modules. First, an improved kernelized correlation filter model in real-time tracking module was adopted to track the contact region. Then the pixel-level detection module was used to detect contact point in contact region via the proposed contact point regression residual network (CPRR-Net). Finally, a filter-based optimization module was added to correct the contact position using the Kalman filter. This work additionally employed a new rail dataset PAC-TPL2020 to prove the effectiveness and feasibility of the proposed multiple strategies in real-world scenarios, and the experimental results demonstrated the robustness and high accuracy (97.07% within 3 pixels and 99.97% within 5 pixels) of our model. It is noteworthy that our mothed runs at 65 frames per second for monitoring PAC contact points.

Unsupervised Indoor Positioning System Based on Environmental Signatures.

Mobile sensors are widely used in indoor positioning in recent years, but most methods require cumbersome calibration for precise positioning results, thus the paper proposes a new unsupervised indoor positioning (UIP) without cumbersome calibration. UIP takes advantage of environment features in indoor environments, as some indoor locations have their signatures. UIP considers these signatures as the landmarks, and combines dead reckoning with them in a simultaneous localization and mapping (SLAM) frame to reduce positioning errors and convergence time. The test results prove that the system can achieve accurate indoor positioning, which highlights its prospect as an unconventional method of indoor positioning.

Site-Specific Unmodeled Error Mitigation for GNSS Positioning in Urban Environments Using a Real-Time Adaptive Weighting Model

In Global Navigation Satellite System (GNSS) positioning, observation precisions are frequently impacted by the site-specific unmodeled errors, especially for the code observations that are widely used by smart phones and vehicles in urban environments. The site-specific unmodeled errors mainly refer to the multipath and other space loss caused by the signal propagation (e.g., non-line-of-sight reception). As usual, the observation precisions are estimated by the weighting function in a stochastic model. Only once the realistic weighting function is applied can we obtain the precise positioning results. Unfortunately, the existing weighting schemes do not fully take these site-specific unmodeled effects into account. Specifically, the traditional weighting models indirectly and partly reflect, or even simply ignore, these unmodeled effects. In this paper, we propose a real-time adaptive weighting model to mitigate the site-specific unmodeled errors of code observations. This unmodeled-error-weighted model takes full advantages of satellite elevation angle and carrier-to-noise power density ratio (C/N0). In detail, elevation is taken as a fundamental part of the proposed model, then C/N0 is applied to estimate the precision of site-specific unmodeled errors. The principle of the second part is that the measured C/N0 will deviate from the nominal values when the signal distortions are severe. Specifically, the template functions of C/N0 and its precision, which can estimate the nominal values, are applied to adaptively adjust the precision of site-specific unmodeled errors. The proposed method is tested in single-point positioning (SPP) and code real-time differenced (RTD) positioning by static and kinematic datasets. Results indicate that the adaptive model is superior to the equal-weight, elevation and C/N0 models. Compared with these traditional approaches, the accuracy of SPP and RTD solutions are improved by 35.1% and 17.6% on average in the dense high-rise building group, as well as 11.4% and 11.9% on average in the urban-forested area. This demonstrates the benefit to code-based positioning brought by a real-time adaptive weighting model as it can mitigate the impacts of site-specific unmodeled errors and improve the positioning accuracy.

Scan-to-BIM for ‘secondary’ building components

Works dealing with Scan-to-BIM have, to date, principally focused on 'structural' components such as floors, ceilings and walls (with doors and windows). But the control of new facilities and the production of their corresponding as-is BIM models requires the identification and inspection of numerous other building components and objects, e.g. MEP components, such as plugs, switches, ducts, and signs. In this paper, we present a new 6D-based (XYZ + RGB) approach that processes dense coloured 3D points provided by terrestrial laser scanners in order to recognize the aforementioned smaller objects that are commonly located on walls. This paper focuses on the recognition of objects such as sockets, switches, signs, extinguishers and others. After segmenting the point clouds corresponding to the walls of a building, a set of candidate objects are detected independently in the colour and geometric spaces, and an original consensus procedure integrates both results in order to infer recognition. Finally, the recognized object is positioned and inserted in the as-is semantically-rich 3D model, or BIM model. The assessment of the method has been carried out in simulated scenarios under virtual scanning providing high recognition rates and precise positioning results. Experimental tests in real indoors using our MoPAD (Mobile Platform for Autonomous Digitization) platform have also yielded promising results.

Selected properties of GPS and Galileo-IOV receiver intersystem biases in multi-GNSS data processing

Two overlapping frequencies—L1/E1 and L5/E5a—in GPS and Galileo systems support the creation of mixed double-differences in a tightly combined relative positioning model. On the other hand, a tightly combined model makes it necessary to take into account receiver intersystem bias, which is the difference in receiver hardware delays. This bias is present in both carrier-phase and pseudorange observations. Earlier research showed that using a priori knowledge of earlier-calibrated ISB to correct GNSS observations has significant impact on ambiguity resolution and, therefore, precise positioning results. In previous research concerning ISB estimation conducted by the authors, small oscillations in phase ISB time series were detected. This paper investigates this effect present in the GPS–Galileo-IOV ISB time series. In particular, ISB short-term temporal stability and its dependence on the number of Galileo satellites used in the ISB estimation was examined. In this contribution we investigate the amplitude and frequency of the detected ISB time series oscillations as well as their potential source. The presented results are based on real observational data collected on a zero baseline with the use of different sets of GNSS receivers.

DPM 2D Bar Code Locating based on Corner Detection and Clustering Analysis

Industrial DPM bar code is achieved by means of laser etching on metal surface; it uses Data Matrix bar code image as the main carrier, which can ensure the full life cycle tracking ability. But due to the ambient light and metal materials, collected industrial DPM images may exist uneven illumination, low contrast and other issues. How to identify this code type quickly and accurately is a problem, and how to locate the bar code area accurately is even more critical and difficult. In this paper, according to the characteristics of frequently appeared cartesian points in DPM bar code area, an adaptive corner detection method based on curvature scale space is used to detect the corners effectively. Then for the corners gathered by clusters, an improved density-based clustering method is proposed to achieve precise positioning results. Experimental results show that the proposed algorithm has certain suppression ability for low contrast, illumination and blur deformation images and is superior to the traditional algorithms on positioning precision and accuracy.

A Large-panel Two-CCD Camera Coordinate System with an Alternate-Eight-Matrix Look-Up-Table Method

This study proposed a novel positioning model, composing of a two-camera calibration system and an Alternate-Eight-Matrix (AEM) Look-Up-Table (LUT). Two video cameras were fixed on two sides of a large-size screen to solve the problem of field of view. The first to the fourth LUTs were used to compute the corresponding positions of specified regions on the screen captured by the camera on the right side. In these four LUTs, the coordinate mapping data of the target were stored in two matrixes, while the gray level threshold values of different positions were stored in other matrixes. Similarly, the fifth to the eighth LUTs were used to compute the corresponding positions of the specified regions on the screen captured by the camera on the left side. Experimental results showed that the proposed model can solve the problems of dead zones and non-uniform light fields, while achieving rapid and precise positioning results.

A comparative study of the integer ambiguity validation procedures

In GPS and GLONASS satellite-based positioning, the correct determination of the integer carrier phase ambiguities is the key to achieve precise positioning results. The process of determining the ambiguities, called ambiguity resolution, is usually separated into three steps: (a) estimating the float or real-valued ambiguities, (b) searching the best integer ambiguity set, (c) validating the best ambiguity set. Whilst the theory and methodology for ambiguity estimation and search are well documented, the ambiguity validation issue is still under investigation. Existing ambiguity validation procedures are based on various statistical assumptions and therefore, may have different performances in practical applications. In this paper, the major ambiguity validation procedures are analysed and their performances in both GPS and GLONASS ambiguity resolution are numerically compared. It is concluded that both the probability of estimating ambiguities correctly and confidence levels of the ambiguity discrimination tests are both important indicators of the reliability of ambiguity resolution.

High-Precision Real-Time GPS Positioning Concepts: Modeling and Results

GPS has been used successfully for a wide range of high-precision surveying applications. Most precise positioning results have been achieved through postprocessing of data. This denies the use of GPS for those surveying and navigation applications which require on-line position computation. A Kalman filtering scheme is presented which is designed to perform high-integrity, real-time GPS relative positioning in static and kinematic modes to centimeter-level accuracy. A continuous-kinematic data set for a train has been processed as an example to explain the operation of the system and illustrate achievable accuracy. Results of the test proved that the repeatability of vertical positions for a train traveling at 120 km/h was better than 5 cm.