Topological Based Scan Matching – Odometry Posterior Sampling in RBPF Under Kinematic Model Failures

Rao-Blackwellized Particle Filters (RBPF) have been utilized to provide a solution to the SLAM problem. One of the main factors that cause RBPF failure is the potential particle impoverishment. Another popular approach to the SLAM problem are Scan Matching methods, whose good results require environments with lots of information, however fail in the lack thereof. To face these issues, in the current work techniques are presented to combine Rao-Blackwellized particle filters with a scan matching algorithm (CRSM SLAM). The particle filter maintains the correct hypothesis in environments lacking features and CRSM is employed in feature-rich environments while simultaneously reduces the particle filter dispersion. Since CRSM’s good performance is based on its high iteration frequency, a multi-threaded combination is presented which allows CRSM to operate while RBPF updates its particles. Additionally, a novel method utilizing topological information is proposed, in order to reduce the number of particle filter resamplings. Finally, we present methods to address anomalous situations where scan matching can not be performed and the vehicle displays behaviors not modeled by the kinematic model, causing the whole method to collapse. Numerous experiments are conducted to support the aforementioned methods’ advantages.     

Line Segment-Based Indoor Mapping with Salient Line Feature Extraction

We present a method of simultaneous localization and mapping (SLAM) in a large indoor environment using a Rao-Blackwellized particle filter (RBPF) along with a line segment as a landmark. To represent the environment in a compact form, we use only two end points of a line segment, thus reducing computational cost in modeling line segment uncertainty. With a modified scan point clustering method, the proposed adaptive iterative end point fitting contributes to the estimation of line parameters by considering noisy scan points near end points. Thus, by line segment matching the robot is localized well in a local frame. We also introduce an online and offline method of global line merging, which provides a more compact map by removing spurious lines and merging collinear lines. Each of our approaches is efficiently integrated into the proposed RBPF-SLAM framework. In experiments with well-known data sets, the proposed method provides reliable SLAM and compact map representation even in a cluttered environment.     

基于分布式感知的移动机器人同时定位与地图创建

为了创建大规模环境的精确栅格地图,提出一种基于分布式感知的两层同时定位与地图创建（SLAM）算法．在局部层,机器人一旦进入了一个新的摄像头视野,便依据机器人本体上的激光和里程计信息,采用Rao-Blackwellized粒子滤波方法创建一个新的局部栅格地图．与此同时,带有检测标志的机器人在摄像头视野内以曲线方式运动,以解决该摄像头的标定问题．在全局层,一系列的局部地图组成一个连接图,局部地图间的约束对应于连接图的边．为了生成一个准确且全局一致的环境地图,采用随机梯度下降法对连接图进行优化．实验结果验证了所提算法的有效性．     

Improved Techniques for Grid Mapping With Rao-Blackwellized Particle Filters

Recently, Rao-Blackwellized particle filters (RBPF) have been introduced as an effective means to solve the simultaneous localization and mapping problem. This approach uses a particle filter in which each particle carries an individual map of the environment. Accordingly, a key question is how to reduce the number of particles. In this paper, we present adaptive techniques for reducing this number in a RBPF for learning grid maps. We propose an approach to compute an accurate proposal distribution, taking into account not only the movement of the robot, but also the most recent observation. This drastically decreases the uncertainty about the robot's pose in the prediction step of the filter. Furthermore, we present an approach to selectively carry out resampling operations, which seriously reduces the problem of particle depletion. Experimental results carried out with real mobile robots in large-scale indoor, as well as outdoor, environments illustrate the advantages of our methods over previous approaches     

How to localize humanoids with a single camera?

In this paper, we propose a real-time vision-based localization approach for humanoid robots using a single camera as the only sensor. In order to obtain an accurate localization of the robot, we first build an accurate 3D map of the environment. In the map computation process, we use stereo visual SLAM techniques based on non-linear least squares optimization methods (bundle adjustment). Once we have computed a 3D reconstruction of the environment, which comprises of a set of camera poses (keyframes) and a list of 3D points, we learn the visibility of the 3D points by exploiting all the geometric relationships between the camera poses and 3D map points involved in the reconstruction. Finally, we use the prior 3D map and the learned visibility prediction for monocular vision-based localization. Our algorithm is very efficient, easy to implement and more robust and accurate than existing approaches. By means of visibility prediction we predict for a query pose only the highly visible 3D points, thus, speeding up tremendously the data association between 3D map points and perceived 2D features in the image. In this way, we can solve very efficiently the Perspective-n-Point (PnP) problem providing robust and fast vision-based localization. We demonstrate the robustness and accuracy of our approach by showing several vision-based localization experiments with the HRP-2 humanoid robot.     

一种面向实时交互的变形手势跟踪方法

变形手势跟踪是基于视觉的人机交互研究中的一项重要内容.单摄像头条件下,提出一种新颖的变形手势实时跟踪方法.利用一组2D手势模型替代高维度的3D手模型.首先利用贝叶斯分类器对静态手势进行识别,然后对图像进行手指和指尖定位,通过将图像特征与识别结果进行匹配,实现了跟踪过程的自动初始化.提出将K-means聚类算法与粒子滤波相结合,用于解决多手指跟踪问题中手指互相干扰的问题.跟踪过程中进行跟踪状态检测,实现了自动恢复跟踪及手势模型更新.实验结果表明,该方法可以实现对变形手势快速、准确的连续跟踪,能够满足基于视觉的实时人机交互的要求.     

A performance study for camera pose estimation using visual marker based tracking

Vision-based tracking systems are widely used for augmented reality (AR) applications. Their registration can be very accurate and there is no delay between real and virtual scene. However, vision-based tracking often suffers from limited range, errors, heavy processing time and present erroneous behavior due to numerical instability. To address these shortcomings, robust method are required to overcome these problems. In this paper, we survey classic vision-based pose computations and present a method that offers increased robustness and accuracy in the context of real-time AR tracking. In this work, we aim to determine the performance of four pose estimation methods in term of errors and execution time. We developed a hybrid approach that mixes an iterative method based on the extended Kalman filter (EKF) and an analytical method with direct resolution of pose parameters computation. The direct method initializes the pose parameters of the EKF algorithm which performs an optimization of these parameters thereafter. An evaluation of the pose estimation methods was obtained using a series of tests and an experimental protocol. The analysis of results shows that our hybrid algorithm improves stability, convergence and accuracy of the pose parameters.     

移动机器人SLAM关键问题和解决方法综述

从同时定位与地图构建（Simultaneous Localization And Mapping,SLAM）的研究进程出发,通过回顾SLAM近三十年来的研究方法,对移动机器人SLAM的研究进行系统的总结,并指出其存在的三个关键问题.针对这三个问题,介绍了基于概率估计和基于视觉的SLAM方法,对基于概率估计的SLAM实现方法进行对比总结,并对视觉传感器的不同特性对基于视觉的SLAM方法研究进展进行阐述,随后对比分析不同方法的优缺点,讨论了视觉SLAM存在的问题.最后展望SLAM未来的发展方向.     

A strong tracking nonlinear robust filter for eye tracking

Non-intrusive methods for eye tracking are important for many applications of vision-based human computer interaction. However, due to the high nonlinearity of eye motion, how to ensure the robustness of external interference and accuracy of eye tracking pose the primary obstacle to the integration of eye movements into today’s interfaces. In this paper, we present a strong tracking unscented Kalman filter (ST-UKF) algorithm, aiming to overcome the difficulty in nonlinear eye tracking. In the proposed ST-UKF, the Suboptimal fading factor of strong tracking filtering is introduced to improve robustness and accuracy of eye tracking. Compared with the related Kalman filter for eye tracking, the proposed ST-UKF has potential advantages in robustness and tracking accuracy. The last experimental results show the validity of our method for eye tracking under realistic conditions.     

Relocalization based on millimeter wave radar point cloud for visually degraded environments

Simultaneously localization and mapping (SLAM) has been widely used in autonomous mobile systems to fulfill autonomous navigation. Relocalization plays an important role in SLAM for closing the loop and eliminating the drift of pose estimation. Traditional methods mostly rely on LiDAR or camera sensors, which may degrade or even fail in rainy or dusty situations or with large illumination changes. In this article, we explore the use of low-cost commercial millimeter wave (mmWave) radars and propose a noval mmWave radar point cloud-based relocalization method. Our method first pre-processes the radar point cloud and, based on that, achieves fast 3-DOF pose estimation for the robot. We build a prototype and thoroughly evaluate our method using data sets collected by our platform in four complex environments, including street, park, road, and water surface scenarios. The experimental results show that our method consistently outperforms other baseline methods including the vision-based counterparts, especially in the visual degraded scenes.     

Estimations of previewed road curvatures and vehicular motion by a vision-based data fusion scheme

In this study, a new framework of vision-based estimation is developed using some data fusion schemes to obtain previewed road curvatures and vehicular motion states based on the scene viewed from an in-vehicle camera. The previewed curvatures are necessary for the guidance of an automatically steering vehicle, and the desired vehicular motion variables, including lateral deviation, heading angle, yaw rate, and sideslip angle, are also required for proper control of the vehicular lateral motion via steering. In this framework, physical relationships of previewed curvatures among consecutive images, motion variables in terms of image features searched at various levels in the image plane, and dynamic correlation among vehicular motion variables are derived as bases of data fusion to enhance the accuracy of estimation. The vision-based measurement errors are analyzed to determine the fusion gains based on the technique of a Kalman filter such that the measurements from the image plane and predictions of physical models can be properly integrated to obtain reliable estimations. Off-line experimental works using real road scenes are performed to verify the whole framework for image sensing.     

Analysis of Rank-Based Resampling Based on Particle Diversity in the Rao–Blackwellized Particle Filter for Simultaneous Localization and Mapping

In order to solve the simultaneous localization and mapping (SLAM) problem of mobile robots, the Rao–Blackwellized particle filter (RBPF) has been intensively employed. However, it suffers from particle depletion problem, i.e., the number of distinct particles becomes smaller during the SLAM process. As a result, the particles optimistically estimate the SLAM posterior, meaning that particles tend to underestimate their own uncertainty and the filter quickly becomes inconsistent. The main reason of loss of particle diversity is the resampling process of RBPF-SLAM. Standard resampling algorithms for RBPF-SLAM cannot preserve particle diversity due to the behavior of their removing and replicating particles. Thus, we propose rank-based resampling (RBR), which assigns selection probabilities to resample particles based on the rankings of particles. In addition, we provide an extensive analysis on the performance of RBR, including scheduling of resampling. Through the simulation results, we show that the estimation capability of RBPF-SLAM by RBR outperforms that by standard resampling algorithms. More importantly, RBR preserves particle diversity much longer, so it can prevent a certain particle from dominating the particle set and reduce the estimation errors. In addition, through consistency tests, it is shown that RBPF-SLAM by the standard resampling algorithms is optimistically inconsistent, but RBPF-SLAM by RBR is so pessimistically inconsistent that it gives a chance to reduce the estimation errors.     

A new approach to solve SLAM challenges by relative map filter

In this paper we propose a new approach to solve some challenges in the simultaneous localization and mapping (SLAM) problem based on the relative map filter (RMF). This method assumes that the relative distances between the landmarks of relative map are estimated fully independently. This considerably reduces the computational complexity to average number of landmarks observed in each scan. To solve the ambiguity that may happen in finding the absolute locations of robot and landmarks, we have proposed two separate methods, the lowest position error (LPE) and minimum variance position estimator (MVPE). Another challenge in RMF is data association problem where we also propose an algorithm which works by using motion sensors without engaging in their cumulative error. To apply these methods, we switch successively between the absolute and relative positions of landmarks. Having a sufficient number of landmarks in the environment, our algorithm estimates the positions of robot and landmarks without using motion sensors and kinematics of robot. Motion sensors are only used for data association. The empirical studies on the proposed RMF-SLAM algorithm with the LPE or MVPE methods show a better accuracy in localization of robot and landmarks in comparison with the absolute map filter SLAM.     

Invariant surface and motion estimation from sparse range data

In this paper, we present a system for the estimation of the surface structure and the motion parameters of a free-flying object in a tele-robotics experiment. The system consists of two main components: (i) a vision-based invariant-surface and motion estimator and (ii) a Kalman filter state estimator. We present a new algorithm for motion estimation from sparse multi-sensor range data. The motion estimates from the vision-based estimator are input to a Kalman filter state estimator for continuously tracking a free-flying object in space under zero-gravity conditions. The predicted position and orientation parameters are then fed back to the vision module of the system and serve as an initial guess in the search for optimal motion parameters. The task of the vision module is two-fold: (i) estimating a piecewise-smooth surface from a single frame of multi-sensor data and (ii) determining the most likely (in the Bayesian sense) object motion that makes data in subsequent time frames to have been sampled from the same piecewise-smooth surface. With each incoming data frame, the piecewise-smooth surface is incrementally refined. The problem is formulated as an energy minimization and solved numerically resulting in a surface estimate invariant to 3D rigid motion and the vector of motion parameters. Performance of the system is depicted on simulated and real range data.     

A sensor-based SLAM algorithm for camera tracking in virtual studio

This paper addresses a sensor-based simultaneous localization and mapping （SLAM） algorithm for camera tracking in a virtual studio environment. The traditional camera tracking methods in virtual studios are vision-based or sensor-based. However, the chroma keying process in virtual studios requires color cues, such as blue background, to segment foreground objects to be inserted into images and videos. Chroma keying limits the application of vision-based tracking methods in virtual studios since the background cannot provide enough feature information. Furthermore, the conventional sensor-based tracking approaches suffer from the jitter, drift or expensive computation due to the characteristics of individual sensor system. Therefore, the SLAM techniques from the mobile robot area are first investigated and adapted to the camera tracking area. Then, a sensor-based SLAM extension algorithm for two dimensional （2D） camera tracking in virtual studio is described. Also, a technique called map adjustment is proposed to increase the accuracy＇ and efficiency of the algorithm. The feasibility and robustness of the algorithm is shown by experiments. The simulation results demonstrate that the sensor-based SLAM algorithm can satisfy the fundamental 2D camera tracking requirement in virtual studio environment.     

A Sensor-based SLAM Algorithm for Camera Tracking vin Virtual Studio

This paper addresses a sensor-based simultaneous localization and mapping (SLAM) algorithm for camera tracking in a virtual studio environment. The traditional camera tracking methods in virtual studios are vision-based or sensor-based. However, the chroma keying process in virtual studios requires color cues, such as blue background, to segment foreground objects to be inserted into images and videos. Chroma keying limits the application of vision-based tracking methods in virtual studios since the background cannot provide enough feature information. Furthermore, the conventional sensor-based tracking approaches suffer from the jitter, drift or expensive computation due to the characteristics of individual sensor system. Therefore, the SLAM techniques from the mobile robot area are first investigated and adapted to the camera tracking area. Then, a sensor-based SLAM extension algorithm for two dimensional (2D) camera tracking in virtual studio is described. Also, a technique called map adjustment is proposed to increase the accuracy and efficiency of the algorithm. The feasibility and robustness of the algorithm is shown by experiments. The simulation results demonstrate that the sensor-based SLAM algorithm can satisfy the fundamental 2D camera tracking requirement in virtual studio environment.     

A Modified Particle Filter for Simultaneous Localization and Mapping

The implementation of a particle filter (PF) for vision-based bearing-only simultaneous localization and mapping (SLAM) of a mobile robot in an unstructured indoor environment is presented in this paper. Variations, using techniques from the genetic algorithm (GA), to standard PF procedures are proposed to alleviate the sample impoverishment problem. A monochrome CCD camera mounted on the robot is used as the measuring device and a measure on the image quality is incorporated into data association and PF update. Since the bearing-only measurement does not contain range information, we add a pseudo range to the measurement during landmark initialization as a hypothesised pair and the non-promising landmark is removed by a map management strategy. Simulation and experimental results from an implementation using real-life data acquired from a Pioneer robot are included to demonstrate the effectiveness of our approach.     

The constrained SLAM framework for non-instrumented augmented reality

This paper addresses the challenging issue of marker less tracking for Augmented Reality. It proposes a real-time camera localization in a partially known environment, i.e. for which a geometric 3D model of one static object in the scene is available. We propose to take benefit from this geometric model to improve the localization of keyframe-based SLAM by constraining the local bundle adjustment process with this additional information. We demonstrate the advantages of this solution, called contrained SLAM, on both synthetic and real data and present very convincing augmentation of 3D objects in real-time. Using this tracker, we also propose an interactive augmented reality system for training application. This system, based on a Optical See-Through Head Mounted Display, allows to augment the users vision field with virtual information accurately co-registered with the real world. To keep greatly benefit of the potential of this hand free device, the system combines the tracker module with a simple user-interaction vision-based module to provide overlaid information in response to user requests.     

基于激光和视觉信息的机器人目标跟踪方法

文中介绍了一种利用移动机器人的激光信息和摄像头信息实时跟踪目标的方法。实现了对人的准确迅速的跟踪。通过大量提取照到人的双脚的激光特征作为样本集,描述了一种基于条件随机场（CRF）模型的Rao—Blackwellized particle filter（RBPF）算法,CRF的observation potential可以直接从样本数据中获得。采用类似栅格滤波方法计算样本的后验概率。RBPF算法根据后验概率进行权值的更新和采样实现对激光特征的实时跟踪,从而实现人的跟踪。根据人的位置信息可以确定人在摄像头图像窗口中的大概位置,提取该位置的SURF特征,从而获得人在图像中的精确位置。