Efficient and accurate stereo matching for cloth manipulation

Due to the recent development of robotic techniques, researching robots that can assist in everyday household tasks, especially robotic cloth manipulation has become popular in recent years. Stereo matching forms a crucial part of the robotic vision and aims to derive depth information from image pairs captured by the stereo cameras. Although stereo robotic vision is widely adopted for cloth manipulation robots in the research community, this remains a challenging research task. Robotic vision requires very accurate depth output in a relatively short timespan in order to successfully perform cloth manipulation in real-time. In this thesis, we mainly aim to develop a robotic stereo matching based vision system that is both efficient and effective for the task of robotic cloth manipulation. Effectiveness refers to the accuracy of the depth map generated from the stereo matching algorithms for the robot to grasp the required details to achieve the given task on cloth materials while efficiency emphasizes the required time for the stereo matching to process the images. With respect to efficiency, firstly, by exploring a variety of different hardware architectures such as multi-core CPU and graphic processors (GPU) to accelerate stereo matching, we demonstrate that the parallelised stereo-matching algorithm can be significantly accelerated, achieving 12X and 176X speed-ups respectively for multi-core CPU and GPU, compared with SISD (Single Instruction, Single Data) single-thread CPU. In terms of effectiveness, due to the fact that there are no cloth based testbeds with depth map ground-truths for evaluating the accuracy of stereo matching performance in this context, we created five different testbeds to facilitate evaluation of stereo matching in the context of cloth manipulation. In addition, we adapted a guided filtering algorithm into a pyramidical stereo matching framework that works directly for unrectified images, and evaluate its accuracy utilizing the created cloth testbeds. We demonstrate that our proposed approach is not only efficient, but also accurate and suits well to the characteristics of the task of cloth manipulations. This also shows that rather than relying on image rectification, directly applying stereo matching to unrectified images is effective and efficient. Finally, we further explore whether we can improve efficiency while maintaining reasonable accuracy for robotic cloth manipulations (i.e.~trading off accuracy for efficiency). We use a foveated matching algorithm, inspired by biological vision systems, and found that it is effective in trading off accuracy for efficiency, achieving almost the same level of accuracy for both cloth grasping and flattening tasks with two to three fold acceleration. We also demonstrate that with the robot we can use machine learning techniques to predict the optimal foveation level in order to accomplish the robotic cloth manipulation tasks successfully and much more efficiently. To summarize, in this thesis, we extensively study stereo matching, contributing to the long-term goal of developing effective ways for efficient whilst accurate robotic stereo matching for cloth manipulation

The Revisiting Problem in Simultaneous Localization and Mapping: A Survey on Visual Loop Closure Detection

Where am I? This is one of the most critical questions that any intelligent system should answer to decide whether it navigates to a previously visited area. This problem has long been acknowledged for its challenging nature in simultaneous localization and mapping (SLAM), wherein the robot needs to correctly associate the incoming sensory data to the database allowing consistent map generation. The significant advances in computer vision achieved over the last 20 years, the increased computational power, and the growing demand for long-term exploration contributed to efficiently performing such a complex task with inexpensive perception sensors. In this article, visual loop closure detection, which formulates a solution based solely on appearance input data, is surveyed. We start by briefly introducing place recognition and SLAM concepts in robotics. Then, we describe a loop closure detection system's structure, covering an extensive collection of topics, including the feature extraction, the environment representation, the decision-making step, and the evaluation process. We conclude by discussing open and new research challenges, particularly concerning the robustness in dynamic environments, the computational complexity, and scalability in long-term operations. The article aims to serve as a tutorial and a position paper for newcomers to visual loop closure detection.Comment: 25 pages, 15 figure

GPU Implementation of Multi-View Stereo Algorithms

Tohoku University青木孝

Motion stereo at sea: Dense 3D reconstruction from image sequences monitoring conveyor systems on board fishing vessels

A system that reconstructs 3D models from a single camera monitoring fish transported on a conveyor system is investigated. Models are subsequently used for training a species classifier and for improving estimates of discarded biomass. It is demonstrated that a monocular camera, combined with a conveyor's linear motion produces a constrained form of multiview structure from motion, that allows the 3D scene to be reconstructed using a conventional stereo pipeline analogous to that of a binocular camera. Although motion stereo was proposed several decades ago, the present work is the first to compare the accuracy and precision of monocular and binocular stereo cameras monitoring conveyors and operationally deploy a system. The system exploits Convolutional Neural Networks (CNNs) for foreground segmentation and stereo matching. Results from a laboratory model show that when the camera is mounted 750 mm above the conveyor, a median accuracy of <5 mm can be achieved with an equivalent baseline of 62 mm. The precision is largely limited by error in determining the equivalent baseline (i.e. distance travelled by the conveyor belt). When ArUco markers are placed on the belt, the inter quartile range (IQR) of error in z (depth) near the optical centre was found to be ±4 mm

Data mining based learning algorithms for semi-supervised object identification and tracking

Sensor exploitation (SE) is the crucial step in surveillance applications such as airport security and search and rescue operations. It allows localization and identification of movement in urban settings and can significantly boost knowledge gathering, interpretation and action. Data mining techniques offer the promise of precise and accurate knowledge acquisition techniques in high-dimensional data domains (and diminishing the “curse of dimensionality” prevalent in such datasets), coupled by algorithmic design in feature extraction, discriminative ranking, feature fusion and supervised learning (classification). Consequently, data mining techniques and algorithms can be used to refine and process captured data and to detect, recognize, classify, and track objects with predictable high degrees of specificity and sensitivity. Automatic object detection and tracking algorithms face several obstacles, such as large and incomplete datasets, ill-defined regions of interest (ROIs), variable scalability, lack of compactness, angular regions, partial occlusions, environmental variables, and unknown potential object classes, which work against their ability to achieve accurate real-time results. Methods must produce fast and accurate results by streamlining image processing, data compression and reduction, feature extraction, classification, and tracking algorithms. Data mining techniques can sufficiently address these challenges by implementing efficient and accurate dimensionality reduction with feature extraction to refine incomplete (ill-partitioning) data-space and addressing challenges related to object classification, intra-class variability, and inter-class dependencies. A series of methods have been developed to combat many of the challenges for the purpose of creating a sensor exploitation and tracking framework for real time image sensor inputs. The framework has been broken down into a series of sub-routines, which work in both series and parallel to accomplish tasks such as image pre-processing, data reduction, segmentation, object detection, tracking, and classification. These methods can be implemented either independently or together to form a synergistic solution to object detection and tracking. The main contributions to the SE field include novel feature extraction methods for highly discriminative object detection, classification, and tracking. Also, a new supervised classification scheme is presented for detecting objects in urban environments. This scheme incorporates both novel features and non-maximal suppression to reduce false alarms, which can be abundant in cluttered environments such as cities. Lastly, a performance evaluation of Graphical Processing Unit (GPU) implementations of the subtask algorithms is presented, which provides insight into speed-up gains throughout the SE framework to improve design for real time applications. The overall framework provides a comprehensive SE system, which can be tailored for integration into a layered sensing scheme to provide the war fighter with automated assistance and support. As more sensor technology and integration continues to advance, this SE framework can provide faster and more accurate decision support for both intelligence and civilian applications

The New Hampshire, Vol. 74, No. 43 (Apr. 10, 1984)

The student publication of the University of New Hampshire

Maximum similarity based feature matching and adaptive multiple kernel learning for object recognition

In this thesis, we perform object recognition using (i) maximum similarity based feature matching, and (ii) adaptive multiple kernel learning. Images are likely more similar if they contain objects within the same categories, so how to measure image similarities correctly and efficiently is one of the critical issues for object recognition. We first propose to match features between two images so that their similarity is maximized, and employ support vector machines (SVMs) for recognition based on the maximum similarity matrix. Secondly, given several similarity matrices (kernels) created by different visual information in images, we propose a novel adaptive multiple kernel learning technique to generate an optimal kernel from all the kernels based on biconvex optimization. These two new approaches are tested on the most recent image benchmark datasets and their results are impressive, equalling or bettering the state-of-the-art results

An Optical Flow Odometry Sensor Based on the Raspberry Pi Computer

Diplomová práce popisuje návrh a implementaci odometrického senzoru vhodného pro malé bezpilotní létající prostředky. Senzor je založen na jednodeskovém počítači s operačním systémem Linux a kameře směřující k zemi. Počítac obsahuje hardwarový grafický čip, který během kódováni videa počítá optický tok. Optický tok je spolu s informací ze senzoru vzdálenosti použit pro odhad aktuální rychlosti pohybu. Senzor byl porovnán s existujícím řešením a otestován v místnosti i ve venkovním prostředí. Práce také navrhuje alternativní softwarová řešení, která nejsou pevně svázána se specifickou hardwarovou implementací počítače.The thesis describes the design and implementation of an odometry sensor suitable for micro aerial vehicles. The sensor is based on a ground-facing camera and a single-board Linux-based embedded computer with a multimedia SoC. The SoC features a hardware video encoder which is used to estimate optical flow in a real-time. The optical flow is then used in combination with a distance sensor to estimate vehicle's velocity. The proposed sensor is compared to a similar existing solution and evaluated in both indoor and outdoor environments. Moreover, alternative software approaches, independent of the selected board's specific hardware and firmware implementation, are also proposed