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A list of all the posts and pages found on the site. For you robots out there is an XML version available for digesting as well.
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Posts
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Blog Post number 4
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Blog Post number 2
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Blog Post number 1
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portfolio
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publications
GLIO: Tightly-Coupled GNSS/LiDAR/IMU Integration for Continuous and Drift-Free State Estimation of Intelligent Vehicles in Urban Areas
Published in IEEE Transactions on Intelligent Vehicles (T-IV), 2023
This paper is about the number 1. The number 2 is left for future work.
Recommended citation: X. Liu, W. Wen and L. -T. Hsu, "GLIO: Tightly-Coupled GNSS/LiDAR/IMU Integration for Continuous and Drift-Free State Estimation of Intelligent Vehicles in Urban Areas," in IEEE Transactions on Intelligent Vehicles, vol. 9, no. 1, pp. 1412-1422, Jan. 2024, doi: 10.1109/TIV.2023.3323648. https://ieeexplore.ieee.org/abstract/document/10285475
talks
Presentation in ION GNSS+ 2022
Published:
Global navigation satellite system (GNSS) real-time kinematic (RTK) has shown centimeter-level absolute positioning results in open-sky areas. However, it is also known to suffer from polluted GNSS measurements and poor satellite geometry in urban canyons, because of the non-line-of-sight and multipath reception caused by the signal blockage and reflection. Light detection and ranging (LiDAR) sensors, along with LiDAR/inertial measurement unit (IMU) odometry systems, can provide precise environment description and short-term accurate relative positioning capability, which could be utilized for aiding GNSS-RTK to obtain better performance. The recently developed 3D LiDAR-aided GNSS-RTK positioning methods detected the GNSS NLOS receptions via the incrementally built map and improve the satellite geometry using the low-lying virtual satellite from LiDAR features. However, the high-elevation angle NLOS receptions cannot be fully detected and the multipath signals cannot be effectively mitigated. To fill this gap, this paper proposes a 3D LiDAR aided GNSS-RTK positioning method via iterated coarse to fine batch optimization by (1) Global 3D point cloud map aided NLOS exclusion which enables the detection of high-elevation angle NLOS receptions. (2) Iterated batch optimization based on a innovatively devised tightly-coupled factor graph which fully exploits the global consistency among the constraints of LiDAR, IMU and GNSS-RTK to exclude the potential multipath signals. Our proposed method aims to achieve lifelong accurate positioning performance in deeply urbanized areas. The effectiveness of the proposed method has been proved by the evaluation conducted on our open-source challenging dataset, UrbanNav, which contains various sequences collected by automobile-level low-cost GNSS receivers in urban canyons of Hong Kong.
Presentation in ION GNSS+ 2023
Published:
Global Navigation Satellite System (GNSS) plays a crucial role in modern navigation systems, but its effectiveness is significantly challenged in urban environments due to the non-line-of-sight (NLOS) signal caused by reflection. In this paper, to essentially alleviate the NLOS problem, we propose an accurate NLOS correction method by Doppler-aided direction-of-arrival (DOA) estimation and 3D LiDAR-aided reflection restoration. For the first point, we propose a Doppler-aided optimization-based DOA estimation method that only requires receiver velocity. For the second point, we extend our conventional 3DLA GNSS to propose a 3D LiDAR-aided reflection restoration method including reflection point searching, correction formulation, and validation for reliable NLOS correction. Different from the conventional model-, or LiDAR-based NLOS correction methods, the proposed method does not rely on the shortest path assumption and therefore is able to correct NLOS receptions with errors exceeding 100 meters. The proposed method is evaluated using a representative urban canyon dataset and its effectiveness is proven by a nearly 80% average NLOS correction ratio and over 80% positioning accuracy improvement.
teaching
AAE4109 Aircraft Maintenance Practices
Teaching Assistant in Undergraduate Course, The Hong Kong Polytechnic University, Department of Aeronautical and Aviation Engineering, 2022
To provide students with knowledge of aircraft maintenance practice and application in modern aircraft maintenance.
AAE5105 FLEET MANAGEMENT AND AVIATION SUSTAINABILITY
Teaching Assistant, The Hong Kong Polytechnic University, Department of Aeronautical and Aviation Engineering, 2023
This subject will provide students with 1. advanced airline fleet management, crew pairing and fatigue management; and 2. the advanced engines types, aviation fuel, emission mitigation strategy, sustainable aviation system in airline aspect.