Huijing Zhao

Tracking Generic Human Motion via Fusion of Low- and High-Dimensional Approaches

Tracking generic human motion is highly challenging due to its high-dimensional state space and the various motion types involved. In order to deal with these challenges, a fusion formulation which integrates low- and high-dimensional tracking approaches into one framework is proposed. The low-dimensional approach successfully overcomes the high-dimensional problem of tracking the motions with available training data by learning motion models, but it only works with specific motion types. On the other hand, although the high-dimensional approach may recover the motions without learned models by sampling directly in the pose space, it lacks robustness and efficiency. Within the framework, the two parallel approaches, low- and high-dimensional, are fused via a probabilistic approach at each time step. This probabilistic fusion approach ensures that the overall performance of the system is improved by concentrating on the respective advantages of the two approaches and resolving their weak points. The experimental results, after qualitative and quantitative comparisons, demonstrate the effectiveness of the proposed approach in tracking generic human motion.

Reconstructing Textured CAD Model of Urban Environment Using Vehicle-Borne Laser Range Scanners and Line Cameras

In this paper, a novel method is presented to generate textured CAD model of out-door urban environment using a vehicle-borne sensor system. In data measurement, three single-row laser range scanners and six line cameras are mounted on a measurement vehicle, which has been equipped with a GPS/INS/Odometer based navigation system. Laser range and line images are measured as the vehicle moves ahead. They are synchronized with the navigation system, so that can be geo-referenced to a world coordinate system. Generation of CAD model is conducted in two steps. A geometric model is first generated using the geo-referenced laser range data, where urban features like buildings, ground surface and trees are extracted in a hierarchical way. Different urban features are represented using different geometric primitives like planar face, TIN and triangle. Texture of the urban features is generated by projecting and re-sampling line images on the geometric model. An out-door experiment is conducted, and a textured CAD model of a real urban environment is reconstructed in a full automatic mode.

A vehicle-borne urban 3-D acquisition system using single-row laser range scanners

In this research, a novel vehicle-borne system of measuring three-dimensional (3-D) urban data using single-row laser range scanners is proposed. Two single-row laser range scanners are mounted on the roof of a vehicle, doing horizontal and vertical profiling respectively. As the vehicle moves ahead, a horizontal and a vertical range profile of the surroundings are captured at each odometer trigger. The freedom of vehicle motion is reduced from six to three by assuming that the ground surface is flat and smooth so resulting in the vehicle moving on almost the same horizontal plane. Horizontal range profiles, which have an overwhelming overlay between successive ones, are registered to trace vehicle location and attitude. Vertical range profiles are aligned to the coordinate system of the horizontal one according to the physical geometry between the pair of laser range scanners, and subsequently to a global coordinate system to make up 3-D data. An experiment is conducted where 3-D data of a real urban scene is obtained by registering and integrating 2412 horizontal and vertical range profiles. Two ground truths are used in examination. They are the outputs of a GPS/INS/Odometer based positioning system and a 1:500 digital map of the testing site. Accuracy and efficiency of the method in measuring 3-D urban scene is demonstrated.

Laser-based detection and tracking of multiple people in crowds

Laser-based people tracking systems have been developed for mobile robotic, and intelligent surveillance areas. Existing systems rely on laser point clustering method to extract object locations. However, for dense crowd tracking, laser points of different objects are often interlaced and undistinguishable due to measurement noise and they can not provide reliable features. It causes current systems quite fragile and unreliable. This paper presents a novel and robust laser-based dense crowd tracking method. Firstly, we introduce a stable feature extraction method based on accumulated distribution of successive laser frames. With this method, the noise that generates split and merged measurements is smoothed away and the pattern of rhythmic swing legs is utilized to extract each leg of persons. And then, a region coherency property is introduced to construct an efficient measurement likelihood model. The final tracker is based on the combination of independent Kalman filter and Rao-Blackwellized Monte Carlo data association filter (RBMC-DAF). In real experiments, we obtain raw data from multiple registered laser scanners, which measure two legs for each people on the height of 16cm from horizontal ground. Evaluation with real data shows that the proposed method is robust and effective. It achieves a significant improvement compared with existing laser-based trackers. In addition, the proposed method is much faster than previous works, and can overcome tracking errors resulted from mixed data of two closely situated persons.

Tracking multiple people using laser and vision

We present a novel system that aims at reliably detecting and tracking multiple people in an open area. Multiple single-row laser scanners and one video camera are utilized. Feet trajectory tracking based on registration of distance information from multiple laser scanners and visual body region tracking based on color histogram are combined in a Bayesian formulation. Results from tests in a real environment are reported to demonstrate that the system can detect and track multiple people simultaneously with reliable and real-time performance.

Reconstructing a textured CAD model of an urban environment using vehicle-borne laser range scanners and line cameras

Abstract. In this paper, a novel method is presented for generating a textured CAD model of an outdoor urban environment using a vehicle-borne sensor system. In data measurement, three single-row laser range scanners and six line cameras are mounted on a measurement vehicle, which has been equipped with a GPS/INS/Odometer-based navigation system. Laser range and line images are measured as the vehicle moves forward. They are synchronized with the navigation system so they can be geo-referenced to a world coordinate system. Generation of the CAD model is conducted in two steps. A geometric model is first generated using the geo-referenced laser range data, where urban features, such as buildings, ground surfaces, and trees are extracted in a hierarchical way. Different urban features are represented using different geometric primitives, such as a planar face, a triangulated irregular network (TIN), and a triangle. The texture of the urban features is generated by projecting and resampling line images onto the geometric model. An outdoor experiment is conducted, and a textured CAD model of a real urban environment is reconstructed in a full automatic mode.

Vision-Based Multiple Interacting Targets Tracking via On-Line Supervised Learning

Successful multi-target tracking requires locating the targets and labeling their identities. This mission becomes significantly more challenging when many targets frequently interact with each other (present partial or complete occlusions). This paper presents an on-line supervised learning based method for tracking multiple interacting targets. When the targets do not interact with each other, multiple independent trackers are employed for training a classifier for each target. When the targets are in close proximity or present occlusions, the learned classifiers are used to assist in tracking. The tracking and learning supplement each other in the proposed method, which not only deals with tough problems encountered in multi-target tracking, but also ensures the entire process to be completely on-line. Various evaluations have demonstrated that this method performs better than previous methods when the interactions occur, and can maintain the correct tracking under various complex tracking situations, including crossovers, collisions and occlusions.

Multi-modal tracking of people using laser scanners and video camera

Inspite extensive research on visual tracking of multiple people in computer vision area, the robustness and usability of visual trackers are still discouraging. Recently, a few laser-based detection and tracking methods have been developed in robotics area. However, poor features provided by laser data make the tracker fail in many situations. In this paper, we present a novel method that aims at reliably detecting and tracking multiple people in an open area. Multiple laser scanners and one camera are used as input sensors. In detection stage, laser-based detection algorithm captures newly appeared people and initializes the mean-shift-based visual tracker. In tracking stage, laser-based feet trajectory tracking result and visual body region tracking result are combined with a decision-level Bayesian fusion method. The experimental results demonstrate reliable and real-time performance of the method.

Detection and tracking of multiple pedestrians by using laser range scanners

We propose a novel system for tracking multiple pedestrians in a crowded scene by exploiting single-row laser range scanners that measure distances of surrounding objects. A walking model is built to describe the periodicity of the movement of the feet in the spatial-temporal domain, and a mean-shift clustering technique in combination with spatial- temporal correlation analysis is applied to detect pedestrians. Based on the walking model, particle filter is employed to track multiple pedestrians. Compared with camera-based methods, our system provides a novel technique to track multiple pedestrians in a relatively large area. The experiments, in which over 300 pedestrians were tracked in 5 minutes, show the validity of the proposed system.

SLAM in a dynamic large outdoor environment using a laser scanner

In this research, we propose a method of SLAM in a dynamic large outdoor environment using a laser scanner. Focus are cast on solving two major problems: 1) achieving global accuracy especially in non-cyclical environment, 2) tackling a mixture of data from both dynamic and static objects. Algorithms are developed, where GPS data and control inputs are used to diagnose pose error and guide to achieve a global accuracy; Classification of laser points and objects are conducted not in an independent module but across the processing in a framework of SLAM with moving object detection and tracking. Experiments are conducted using the data from two test-bed vehicles, and performance of the algorithms are demonstrated.