Local Accuracy and Global Consistency for Efficient SLAM

This thesis is concerned with the problem of Simultaneous Localisation and Mapping (SLAM) using visual data only. Given the video stream of a moving camera, we wish to estimate the structure of the environment and the motion of the device most accurately and in real-time. Two effective approaches were presented in the past. Filtering methods marginalise out past poses and summarise the information gained over time with a probability distribution. Keyframe methods rely on the optimisation approach of bundle adjustment, but computationally must select only a small number of past frames to process. We perform a rigorous comparison between the two approaches for visual SLAM. Especially, we show that accuracy comes from a large number of points, while the number of intermediate frames only has a minor impact. We conclude that keyframe bundle adjustment is superior to ltering due to a smaller computational cost. Based on these experimental results, we develop an efficient framework for large-scale visual SLAM using the keyframe strategy. We demonstrate that SLAM using a single camera does not only drift in rotation and translation, but also in scale. In particular, we perform large-scale loop closure correction using a novel variant of pose-graph optimisation which also takes scale drift into account. Starting from this two stage approach which tackles local motion estimation and loop closures separately, we develop a unified framework for real-time visual SLAM. By employing a novel double window scheme, we present a constant-time approach which enables the local accuracy of bundle adjustment while ensuring global consistency. Furthermore, we suggest a new scheme for local registration using metric loop closures and present several improvements for the visual front-end of SLAM. Our contributions are evaluated exhaustively on a number of synthetic experiments and real-image data-set from single cameras and range imaging devices

Hierarchical Reactive Control for Soccer Playing Humanoid Robots

What drives thousands of researchers worldwide to devote their creativity and energy t

Real-time monocular SLAM: Why filter?

Abstract—While the most accurate solution to off-line structure from motion (SFM) problems is undoubtedly to extract as much correspondence information as possible and perform global optimisation, sequential methods suitable for live video streams must approximate this to fit within fixed computational bounds. Two quite different approaches to real-time SFM — also called monocular SLAM (Simultaneous Localisation and Mapping) — have proven successful, but they sparsify the problem in different ways. Filtering methods marginalise out past poses and summarise the information gained over time with a probability distribution. Keyframe methods retain the optimisation approach of global bundle adjustment, but computationally must select only a small number of past frames to process. In this paper we perform the first rigorous analysis of the relative advantages of filtering and sparse optimisation for sequential monocular SLAM. A series of experiments in simulation as well using a real image SLAM system were performed by means of covariance propagation and Monte Carlo methods, and comparisons made using a combined cost/accuracy measure. With some well-discussed reservations, we conclude that while filtering may have a niche in systems with low processing resources, in most modern applications keyframe optimisation gives the most accuracy per unit of computing time. I

SLAM++: Simultaneous Localisation and Mapping at the Level of Objects

We present the major advantages of a new ‘object ori-ented ’ 3D SLAM paradigm, which takes full advantage in the loop of prior knowledge that many scenes consist of repeated, domain-specific objects and structures. As a hand-held depth camera browses a cluttered scene, real-time 3D object recognition and tracking provides 6DoF camera-object constraints which feed into an explicit graph of objects, continually refined by efficient pose-graph opti-misation. This offers the descriptive and predictive power of SLAM systems which perform dense surface reconstruc-tion, but with a huge representation compression. The ob-ject graph enables predictions for accurate ICP-based cam-era to model tracking at each live frame, and efficient ac-tive search for new objects in currently undescribed image regions. We demonstrate real-time incremental SLAM in large, cluttered environments, including loop closure, relo-calisation and the detection of moved objects, and of course the generation of an object level scene description with the potential to enable interaction. 1

Simulation versus single-value estimates in capital expenditure analysis : a comment and analysis / BEBR No. 124

Includes bibliographical references (leaf [9])

Which landmark is useful? Learning selection policies for navigation in unknown environments

Abstract — In general, a mobile robot that operates in unknown environments has to maintain a map and has to determine its own location given the map. This introduces significant computational and memory constraints for most autonomous systems, especially for lightweight robots such as humanoids or flying vehicles. In this paper, we present a novel approach for learning a landmark selection policy that allows a robot to discard landmarks that are not valuable for its current navigation task. This enables the robot to reduce the computational burden and to carry out its task more efficiently by maintaining only the important landmarks. Our approach applies an unscented Kalman filter for addressing the simultaneous localization and mapping problems and uses Monte-Carlo reinforcement learning to obtain the selection policy. Based on real world and simulation experiments, we show that the learned policies allow for efficient robot navigation and outperform handcrafted strategies. We furthermore demonstrate that the learned policies are not only usable in a specific scenario but can also be generalized towards environments with varying properties. I

Multi-cue localization for soccer playing humanoid robots

Abstract. An essential capability of a soccer playing robot is to robustly and accurately estimate its pose on the field. Tracking the pose of a humanoid robot is, however, a complex problem. The main difficulties are that the robot has only a constrained field of view, which is additionally often affected by occlusions, that the roll angle of the camera changes continously and can only be roughly estimated, and that dead reckoning provides only noisy estimates. In this paper, we present a technique that uses field lines, the center circle, corner poles, and goals extracted out of the images of a low-cost wide-angle camera as well as motion commands and a compass to localize a humanoid robot on the soccer field. We present a new approach to robustly extract lines using detectors for oriented line pints and the Hough transform. Since we first estimate the orientation, the individual line points are localized well in the Hough domain. In addition, while matching observed lines and model lines, we do not only consider their Hough parameters. Our similarity measure also takes into account the positions and lengths of the lines. In this way, we obtain a much more reliable estimate how well two lines fit. We apply Monte-Carlo localization to estimate the pose of the robot. The observation model used to evaluate the individual particles considers the differences of expected and measured distances and angles of the other landmarks. As we demonstrate in real-world experiments, our technique is able to robustly and accurately track the position of a humanoid robot on a soccer field. We also present experiments to evaluate the utility of using the different cues for pose estimation.