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Paper:J.L. Blanco's Phd Thesis

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Contributions to Localization, Mapping and Navigation in Mobile Robotics, PhD Thesis, Jose-Luis Blanco-Claraco, November 13th, 2009.
Downloads: PDF (12.6Mb) - Citation (Bibtex) - Slides (17.5 Mb) - Slides+videos (196 Mb)

Paper:Subjective Local Maps for Hybrid Metric-Topological SLAM

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Subjective Local Maps for Hybrid Metric-Topological SLAM, Robotics and Autonomous Systems, 2009 - (PDF).

Abstract: Hybrid maps where local metric sub-maps are kept in the nodes of a graph-based topological structure are gaining relevance as the focus of robot Simultaneous Localization and Mapping (SLAM) shifts towards spatial scalability and long-term operation. In this paper we examine the applicability of spectral graph partitioning techniques to automatically generate metric sub-maps by establishing groups in the sequence of observations gathered by the robot. One of the main aims of this work is to provide a probabilistically grounded interpretation of such a partitioning technique in the context of generating these local maps. We also discuss how to apply it to different kinds of sensory data (stereo images and laser range scans) and how to consider them simultaneously. An important feature of our approach is that it implicitly takes into account the intrinsic characteristics of the sensors, such as the sensor field of view, to perform the partitioning instead of applying heuristics supplied by a human as in other works, and thus the robot builds "subjective" local maps. The ideas presented here are supported by experimental results from a real mobile robot as well as simulations for statistical analysis. We discuss the effects of considering different combinations of sensors in the resulting clustering of the environment.

Paper:A Pure Probabilistic Approach to Range-Only SLAM (ICRA 2008)

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"A Pure Probabilistic Approach to Range-Only SLAM", ICRA 2008, Pasadena (California, USA), May 19-23, 2008. (PDF) - (Slides)

Abstract: Range-Only SLAM (RO-SLAM) represents a difficult problem due to the inherent ambiguity of localizing either the robot or the beacons from distance measurements only. Most previous approaches to this problem employ non-probabilistic batch optimizations or delay the initialization of new beacons within a probabilistic filter until a good estimate is available. The contribution of this work is the formulation of RO-SLAM as an online Bayesian estimation process based on a Rao-Blackwellized Particle Filter. The conditional distribution for each beacon is initialized using an additional particle filter which, eventually, is transformed into an extended Kalman filter when the uncertainty becomes sufficiently small. This approach allows the introduction of new beacons without either delay or any special non-probabilistic processing. We validate our proposal with experiments for both simulated and real datasets.


Paper:An Optimal Filtering Algorithm for Non-Parametric Observation Models in Robot Localization (ICRA 2008)

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"An Optimal Filtering Algorithm for Non-Parametric Observation Models in Robot Localization", ICRA 2008, Pasadena (California, USA), May 19-23, 2008. (PDF) - (Slides)

Abstract: The lack of a parameterized observation model in robot localization using occupancy grids requires the application of sampling-based methods, or particle filters. This work addresses the problem of optimal Bayesian filtering for dynamic systems with observation models that cannot be approximated properly as any parameterized distribution, which includes localization and SLAM with occupancy grids. By integrating ideas from previous works on adaptive sample size, auxiliary particle filters, and rejection sampling, we derive a new particle filter algorithm that enables the usage of the optimal proposal distribution to estimate the true posterior density of a non-parametric dynamic system. Our solution avoids approximations adopted in previous approaches at the cost of a higher computational burden. We present simulations and experimental results for a real robot showing the suitability of the method for localization.

Paper:Extending Obstacle Avoidance Methods through Multiple Parameter-Space Transformations

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"Extending Obstacle Avoidance Methods through Multiple Parameter-Space Transformations", Jose-Luis Blanco, Javier Gonzalez, and Juan-Antonio Fernandez-Madrigal, Autonomous Robots, 2008 - View article - PDF

Abstract:
Obstacle avoidance methods approach the problem of mobile robot autonomous navigation by steering the robot in real-time according to the most recent sensor readings, being suitable to dynamic or unknown environments. However, real-time performance is commonly gained by ignoring the robot shape and some or all of its kinematic restrictions which may lead to poor navigation performance in many practical situations. In this paper we propose a framework where a kinematically constrained and any-shape robot is transformed in real-time into a free-flying point in a new space where well-known obstacle avoidance methods are applicable. Our contribution with this framework is twofold: the definition of generalized space transformations that cover most of the existing transformational approaches, and a reactive navigation system where multiple transformations can be applied concurrently in order to optimize robot motion decisions. As a result, these transformations allow existing obstacle avoidance methods to perform better detection of the surrounding free-space, through “sampling” the space with paths compatible with the robot kinematics. We illustrate how to design these space transformations with some examples from our experience with real robots.

Paper: Malaga dataset 2009 with 6D ground truth

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A Collection of Outdoor Robotic Datasets with centimeter-accuracy Ground Truth, Jose-Luis Blanco, Francisco-Angel Moreno, Javier Gonzalez, Autonomous Robots , 2009 - (Draft PDF) - (Official PDF )

Abstract: The lack of publicly accessible datasets with a reliable ground truth has prevented in the past a fair and coherent comparison of different methods proposed in the mobile robot Simultaneous Localization and Mapping (SLAM) literature. Providing such a ground truth renders specially challenging in the case of visual SLAM, where the world model is 3-dimensional and the robot path is 6-dimensional. This work addresses both the practical and theoretical issues found while building a collection of six outdoor datasets. It is discussed how to estimate the 6-d vehicle path from readings of a set of three Real Time Kinematics (RTK) GPS receivers, as well as the associated uncertainty bounds that can be employed to evaluate the performance of Visual SLAM methods. The vehicle was also equipped with several laser scanners, from which reference point clouds are built as a test-bed for other algorithms such as segmentation or surface fitting. All the datasets, calibration information and associated software tools are available for download.

Erratas (update March 2012):

  • Figure 1(b)  shows the IMU mounted upside down, while it was actually mounted right-side up. Refer to the pictures at the bottom of this page. Notice that yaw,  pitch, roll angles provided in Table 1 are correct (i.e. it was only an issue with the figure).
  • Equation (30) in appendix I fails to mention that adding the angles is only a valid approximation for small rotations.

 

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