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Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Objectives: Real‑time tropospheric mapping functions can be used into real time global navigation satellite system (GNSS) parameter estimation and applications, and it is therefore of great significance to evaluate their modeling accuracy and precise point positioning (PPP) performance. Methods: In this pa‑ per, the slant total delay (STD) modeling accuracy of the latest generation of real time mapping functions, including global pressure and temperature 3 (GPT3), grid‑wise forecast vienna mapping function 3 (VMF3‑ FC) and site ‑wise VMF3‑FC, is evaluated by taking ray ‑traced STD as a reference, and the BDS3 PPP performance of the three mapping functions is analyzed on the coordinate accuracy. Results: The results show that the site‑wise VMF3‑FC persists the best performance with STD accuracy of 2.3 cm at the 30° elevation angle and BDS3 PPP height accuracy of 9.8 mm, and it is recommended to use at the international GNSS service(IGS) stations with the site‑wise products. The performance of the grid‑wise VMF3‑FC is a little worse with the STD accuracy of 2.6 cm and height accuracy of 10.2 mm, and it is recommended as the backup of the site ‑ wise VMF3 ‑FC products. The GPT3 model has the worst performance with the STD accuracy of 7.0 cm and height accuracy of 10.5 mm, while it can be embedded into the positioning software, so it is recommended to use in the case of without the need of external products. [ABSTRACT FROM AUTHOR]

Objectives: The current railway maintenance method is unitary and simple, which is a human force intensive work, requiring tedious and interminable manual check from professional technicians. As a multi‑scale, multi‑probability and long‑term digital representation approach, the digital ‑ twin has seen a rising popularity in engineering construction. Inspired by the convenience of digital‑twin, this paper designs a simultaneous localization and mapping (SLAM) system for railway locomotives. Methods: Unlike traditional mobile mapping system which demands high precision three‑dimensional laser scanning, inertial measurement unit (IMU) / real time kinematic (RTK), as well as complicated post‑processing methods, our solution is capable of real time mapping and odometry visualization through constructed factor graph. The factor graph is a bipartite graph with two node types: Factor nodes and variables nodes, and they are always connected by edges. A new variable node is added to the graph when the pose displacements exceed a certain threshold, then the factor graph is optimized upon the insertion. We use three types of factors for graph construction: IMU preintegration factors, light detection and ranging (LiDAR) odometry factors, RTK factors. Results and Conclusions: The real time performance is further achieved through sliding window optimization. Under more than 300 km field test in various environments, our approach can achieve centimeter‑ lever positioning accuracy in feature rich and low speed cases, and the structures are clearly visible in the real time mapping result. [ABSTRACT FROM AUTHOR]

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Nanjing University of Information Science & Technology (Natural Science Edition) / Nanjing Xinxi Gongcheng Daxue Xuebao (ziran kexue ban) is the property of Editorial Office of Journal of Nanjing University of Information Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Different from other navigation system, there is a divergence between code and phase observables of BeiDou Navigation Satellite System (BDS). In this paper, we analyze the characteristic of code bias variations and propose a polynomial correction model of GEO, IGSO and MEO satellites. Firstly, different stations and different receiver types observables of BeiDou Experiment Tracking Stations (BETS) of Wuhan University,Crustal Movement Observation Network of China (CMONOC) and Multi-GNSS Experiment campaign(MGEX) of IGS are used for analysis and verification. The results show that the code bias variations, which are dependent with satellite types and frequency and independent with receiver type, station position and observation time, vary with satellite elevations. Besides, the code bias variations of satellites may reach up to 1.5 m and can be divided into two groups (GEO/IGSO and MEO). Secondly, based on the analysis of code bias variations of BDS, we established a polynomial correction model of IGSO/MEO code bias variations. Besides, since the elevation of a GEO satellite remains unchanged, we propose to model the single-difference fractional cycle bias with wide-spread ground stations. Then, a correction model for code bias variations of GEO satellites is established by using the consistency of the fractional of wide-lane ambiguity of single-difference between satellites. Finally, the improvement brought by applying our correction model is validated by various strategies, e.g. residual distribution of pseudo-range is more close to normal distribution, and the positioning accuracy of dual-frequency single point positioning as well as single-frequency precise point positioning is improved. [ABSTRACT FROM AUTHOR]

The Japanese QZSS(Quasi-Zenith Satellite System)is a satellite navigation system combing regional assistance with enhancement and covering Japan and surrounding area including partial area of China. The system broadcasts two enhancement signals L1-SAIF and LEX through IGSO and can provide high precision positioning in China region. From the aspects of availability, space signal accuracy and user kinematic PPP(precise point position), this paper comprehensivelyevaluate the performance of QZSS two enhance signals in region of China. With QZS-1 measured data, we executed experiments; the results show that, with 20°cut-off elevation, most areas of China, especially the eastern coastal area can observe the QZSS satellite about 80% of the day; a wide area differential message achieves considerable accuracy when compared with WAAS, as the URE(User Range Error) is about 0.56m and satisfies PPP needs with an accuracy of 1m. The horizontal accuracy is better than 1m; when compared with L1-SAIF, the accuracy of LEX was higher, the accuracy of orbit and clock was decimeter-class. The URE is about 0.4m, achieving sub-meter class positioning with an accuracy of 0.2 m in the horizontal and 0.5 m in the height dimensions. [ABSTRACT FROM AUTHOR]

It is difficult for the BeiDou satellite navigation system to establish a global tracking network abroad, therefore regional tracking station observations are an important tool to achieve precise orbit determination (POD). Our investigation demonstrates that ambiguity resolution and reasonable arc length are important factors for improving the accuracy of regional orbit determination. GPS observations from CMONOC were adopted to simulate regional precise orbit determination; under the condition of the same station distribution, the accuracy of POD with ambiguity resolution was better than 30% with floating solution. Furthermore, the 3D RMS of an orbit with ambiguity resolution using seven stations was about 20 cm, better than the results of an ambiguity float solution using 50 stations. In addition, we evaluated the impact of arc length on POD accuracy from the satellite constellation design and the visible coverage of regional tracking stations. This experiment confirmed that when the observation time of regional stations is more than 48 hours, a valid arc length of regional POD, not less than 24 hours, can always be selected for each GPS satellite; the best selection can achieve a 3D accuracy about 0.3 m. [ABSTRACT FROM AUTHOR]