도심도로에서 자율주행차량의 라이다 기반 강건한 위치 및 자세 추정

학위논문(석사) -- 서울대학교대학원 : 공과대학 기계공학부, 2023. 2. 이경수.This paper presents a method for tackling erroneous odometry estimation results from LiDAR-based simultaneous localization and mapping (SLAM) techniques on complex urban roads. Most SLAM techniques estimate sensor odometry through a comparison between measurements from the current and the previous step. As such, a static environment is generally more advantageous for SLAM systems. However, urban environments contain a significant number of dynamic objects, the point clouds of which can noticeably hinder the performance of SLAM systems. As a countermeasure, this paper proposes a 3D LiDAR SLAM system based on static LiDAR point clouds for use in dynamic outdoor urban environments. The proposed method is primarily composed of two parts, moving object detection and pose estimation through 3D LiDAR SLAM. First, moving objects in the vicinity of the ego-vehicle are detected from a referred algorithm based on a geometric model-free approach (GMFA) and a static obstacle map (STOM). GMFA works in conjunction with STOM to estimate the state of moving objects in real-time. The bounding boxes occupied by these moving objects are utilized to remove points corresponding to dynamic objects in the raw LiDAR point clouds. The remaining static points are applied to LiDAR SLAM. The second part of the proposed method describes odometry estimation through referred LiDAR SLAM, LeGO-LOAM. The LeGO-LOAM, a feature-based LiDAR SLAM framework, converts LiDAR point clouds into range images, from which edge and planar points are extracted as features. The range images are further utilized in a preprocessing stage to improve the computation efficiency of the overall algorithm. Additionally, a 6-DOF transformation is utilized, the model equation of which can be obtained by setting a residual to be the distance between an extracted feature of the current step and the corresponding feature geometry of the previous step. The equation is optimized through the Levenberg-Marquardt method. Furthermore, GMFA and LeGO-LOAM operate in parallel to resolve computational delays associated with GMFA. Actual vehicle tests were conducted on urban roads through a test vehicle equipped with a 32-channel 3D LiDAR and a real-time kinematics GPS (RTK GPS). Validations results have shown the proposed method to significantly decrease estimation errors related to moving feature points while securing target output frequency.본 연구는 복잡한 도심 환경에서 라이다 기반 동시적 위치 추정 및 맵핑(Simultaneous localization and mapping, SLAM)의 이동량 추정 오류를 방지하는 방법론을 제안한다. 대부분의 SLAM은 이전 스텝과 현재 스텝의 센서 측정치를 비교하여 자차량의 이동량을 추정한다. 따라서 SLAM에는 정적인 환경이 필수적이다. 그러나 센서는 도심환경에서 동적인 물체에 쉽게 노출되고 동적 물체로부터 출력되는 라이다 점군들은 이동량 추정 성능을 저하시킬 수 있다. 이에, 본 연구는 동적인 도심환경에서 정적인 점군을 기반한 3차원 라이다 SLAM 시스템을 제안하였다. 제안된 방법론은 이동 물체 인지와 3차원 라이다 SLAM을 통한 위치 및 자세 추정으로 구성된다. 우선, 기하학적 모델 프리 접근법과 정지 장애물 맵의 상호 보완적인 관계에 기반한 참고된 알고리즘을 이용해 자차량 주변의 이동 물체의 동적 상태를 실시간으로 추정한다. 그 후, 추정된 이동 물체가 차지하는 경계선을 이용하여 동적 물체에 해당하는 점들을 기존 라이다 점군에서 제거하고, 결과로 얻은 정적인 라이다 점군은 라이다 SLAM에 입력된다. 다음으로, 제안된 방법론은 라이다 SLAM을 통해 자차량의 위치 및 자세를 추정한다. 이를 위해 본 연구는 라이다 SLAM의 프레임워크인 LeGO-LOAM을 채택하였다. 특징점 기반 SLAM인 LeGO-LOAM은 라이다 점군을 거리 기반 이미지로 변환시켜 특징점인 모서리 점과 평면 점을 추출한다. 또한 거리 기반 이미지를 사용한 전처리 과정을 통해 계산 효율을 높인다. 추출된 현재 스텝의 특징점과 이에 대응되는 이전 스텝의 특징점으로 이루어진 기하학적 구조와의 거리를 잔차로 설정하여 6 자유도 변환식에 대한 모델 방정식을 얻을 수 있다. 참고한 LeGO-LOAM은 해당 방정식을 Levenberg-Marquardt 방법을 통해 최적화를 수행한다. 또한, 본 연구는 참고된 인지 모듈의 처리 지연 문제를 보완하기 위해 이동 물체 인지 모듈과 LeGO-LOAM의 병렬 처리 구조를 고안하였다. 실험은 도심환경에서 32채널 3차원 라이다와 고정밀 GPS를 장착한 실험차량으로 진행되었다. 성능 검증 결과, 제안된 방법은 목표 출력 속도를 보장하면서 움직이는 특징점으로 인한 추정 오차를 유의미하게 줄일 수 있었다.Chapter 1. Introduction １ 1.1. Research Motivation １ 1.2. Previous Research ３ 1.2.1. Moving Object Detection ３ 1.2.2. SLAM ４ 1.3. Thesis Objective and Outline １３ Chapter 2. Methodology １５ 2.1. Moving Object Detection & Rejection １５ 2.1.1. Static Obstacle Map １５ 2.1.2. Geometric Model-Free Approach １８ 2.2. LiDAR SLAM ２２ 2.2.1. Segmentation ２２ 2.2.2. Feature Extraction ２３ 2.2.3. LiDAR Odometry and Mapping ２６ 2.2.4. LiDAR SLAM with Static Point Cloud ２８ Chapter 3. Experiments ３０ 3.1. Experimental Setup ３０ 3.2. Error Metrics ３２ 3.3. LiDAR SLAM using Static Point Cloud ３６ Chapter 4. Conclusion ４４ Bibliography ４５석

납작한 보즈-아인슈타인 응집체에서의 양자 소용돌이 동역학: 양자 난류와 소용돌이 방출

학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부,2016. 2. 신용일.Quantized vortices which are one of elementary excitations in a super uid have long been investigated in Bose condensed systems. Since the first observation of a vortex in a BEC in 1998, experimental researches on vortices have continued including formation of vortices, vortex lattice dynamics and super uid turbulence, etc. Although many issues on vortices already have been investigated due to long history of studies on vortices, there still remain many interesting problems on quantized vortices in a Bose-Einstein condensate. Quantum turbulence (super uid turbulence) has been one of great issues in super uid helium systems. In particular, vortex tangle and its decay dynamics which accompany vortex reconnections are still ongoing issues. Dilute gas of Bose condensed system is a good and new platform to study them. In this thesis, highly oblate BECs have been employed to investigate two dimensional (2D) quantum turbulence, generated by a fastly moving repulsive Gaussian beam, and its decay is interpreted with vortex pair annihilation which is 2D version of vortex reconnection. Our experimental results show that relaxation of super uid turbulence is highly dependent on thermal part of the system. i And this lead us to investigate thermal friction on vortices in finite temperature BECs. Dissipative motion of a vortex in a super uid is described by the interaction between vortex core and thermal component. This is the famous concepts of mutual friction and we measure dimensionless coefficient of mutual friction a using thermal dissipative motion of corotating two vortices. Finally, we study the problem of vortex shedding generated by a ow past a repulsive Gaussian beam. Systematic studies have long been missed on critical velocity vc of a BEC superfuid and we present the detailed measurement on vc for vortex shedding by changing height V0 and radius σ of the Gaussian obstacle. vc shows minimum near V0 ≈ μ, where μ is the chemical potential of the BEC, and monotonically increases for decreasing σ for fixed V0 when V0 >> μ. The results can be understood qualitatively by considering the soft boundary effect of the Gaussian beam. Moreover, we investigate the characteristics of vortex shedding depending on V0 and observe that penetrable beam (V0 μ) is much more prone to irregular vortex shedding. Using this periodic behavior of penetrable beam, we demonstrate a deterministic generation of a single vortex dipole which will enable us to do experiments on such as vortex pair-pair collisions.Chapter 1 Introduction 1 1.1 Ultracold Bose gas and vortex physics 1 1.2 Brief reviews on Bose-Einstein condensates 2 1.3 Vortices in a BEC 4 1.3.1 Quantized vortex in a BEC 4 1.3.2 Angular momentum of a vortex 6 1.3.3 Interaction of two vortices 7 1.4 Outline of the thesis 9 Chapter 2 Quantum turbulence in a BEC 12 2.1 Introduction 12 2.1.1 Decay of a vortex in a superfluid 14 2.2 Experimental methods 15 2.2.1 Generating turbulence in a BEC 15 2.2.2 Vortex number counting 17 2.3 Relaxation of Turbulence 19 2.3.1 Nonexponential decay 19 2.3.2 Vortex pair annihilation 23 2.3.3 Decay rate measurements 26 2.4 Summary and outlook 32 Chapter 3 Mutual friction on quantized vortices in a BEC 38 3.1 Introduction 38 3.1.1 Generation of a doubly charged vortex 40 3.2 Experiments 42 3.3 Theoretical Model 47 3.3.1 Motion of vortices 47 3.3.2 Dynamics of corotating vortices in a harmonic trap 48 3.4 Determination of Mutual friction 52 3.5 Summary 54 Chapter 4 Critical velocity for vortex shedding in a BEC 61 4.1 Introduction 62 4.2 Experiment 65 4.2.1 Calibration of Gaussian beam 69 4.3 Results and Discussion 71 4.4 Summary 77 Chapter 5 Periodic vortex shedding from a moving Gaussian obstacle 82 5.1 Introduction 83 5.2 Experiment 85 5.3 Periodic vortex shedding 86 5.3.1 Penetrable obstacle 86 5.3.2 Impenetrable obstacle 90 5.4 Deterministic generation of a single vortex dipole 93 5.5 Demonstration of a vortex dipole-dipole collision 98 5.6 Possibility of a self-annihilation of a single vortex dipole? 99 5.7 Vortex dipoles vs clustered vortex street 102 5.8 Summary and Outlook 104 Chapter 6 Conclusions and Outlooks 111 Appendices 113 Appendix A Li 교체 진공작업 114 Appendix B Offset lock for 6Li imaging laser 116 Appendix C Measuring trapping frequency with parametric resonance 118 초록 120Docto

Development of Target Vehicle State Estimation Algorithm Using V2V Communication

This paper describes the development of a target vehicle state estimation algorithm using vehicle-to-vehicle (V2V) communication. Perceiving the state of the target vehicle has great importance for successful autonomous driving and has been studied using various sensors and methods for many years. V2V communication has advantage of not being constrained by surrounding circumstances relative to other sensors. In this paper, we adopt the V2V signal for estimating the target vehicle state. Since applying only the V2V signal is improper by its low frequency and latency, the signal is used as additional measured data to improve the estimation accuracy. We estimate the target vehicle state using Extended Kalman filter (EKF); a point mass model was utilized in process update to predict the state of next step. The process update is followed by measurement update when ego vehicle receives V2V information. The proposed study evaluated state estimation by comparing input V2V information in an experiment where the ego vehicle follows the target vehicle behind it.N