Author Archives: Juan-antonio Fernández-madrigal

A new feature for 3D point clouds that is more efficient than the state-of-the-art SHOT

July 26, 2017 08:45 ,

Sai Manoj Prakhya, Bingbing Liu, Weisi Lin, Vinit Jakhetiya & Sharath Chandra Guntuku, B-SHOT: a binary 3D feature descriptor for fast Keypoint matching on 3D point clouds, Auton Robot (2017) 41:1501–1520, DOI: 10.1007/s10514-016-9612-y.

We present the first attempt in creating a binary 3D feature descriptor for fast and efficient keypoint matching on 3D point clouds. Specifically, we propose a linarization technique and apply it on the state-of-the-art 3D feature descriptor, SHOT to create the first binary 3D feature descriptor, which we call B-SHOT. B-SHOT requires 32 times lesser memory for its representation while being six times faster in feature descriptor matching, when compared to the SHOT feature descriptor. Next, we propose a robust evaluation metric, specifically for 3D feature descriptors. A comprehensive evaluation on standard benchmarks reveals that B-SHOT offers comparable keypoint matching performance to that of the state-of-the-art real valued 3D feature descriptors, albeit at dramatically lower computational and memory costs.

Posted in: Computer vision , Tagged: ,

Testbed for comparisons of different UWB sensors applied to localization

July 26, 2017 08:41 ,

A. R. Jiménez Ruiz and F. Seco Granja, “Comparing Ubisense, BeSpoon, and DecaWave UWB Location Systems: Indoor Performance Analysis,” in IEEE Transactions on Instrumentation and Measurement, vol. 66, no. 8, pp. 2106-2117, Aug. 2017.DOI: 10.1109/TIM.2017.2681398.

Most ultrawideband (UWB) location systems already proposed for position estimation have only been individually evaluated for particular scenarios. For a fair performance comparison among different solutions, a common evaluation scenario would be desirable. In this paper, we compare three commercially available UWB systems (Ubisense, BeSpoon, and DecaWave) under the same experimental conditions, in order to do a critical performance analysis. We include the characterization of the quality of the estimated tag-to-sensor distances in an indoor industrial environment. This testing space includes areas under line-of-sight (LOS) and diverse non-LOS conditions caused by the reflection, propagation, and the diffraction of the UWB radio signals across different obstacles. The study also includes the analysis of the estimated azimuth and elevation angles for the Ubisense system, which is the only one that incorporates this feature using an array antenna at each sensor. Finally, we analyze the 3-D positioning estimation performance of the three UWB systems using a Bayesian filter implemented with a particle filter and a measurement model that takes into account bad range measurements and outliers. A final conclusion is drawn about which system performs better under these industrial conditions.

Posted in: Robot sensors , Tagged: ,

A method to model trajectories that captures its essential parameters (for comparisons, clustering, etc.)

July 26, 2017 08:33 ,

W. Lin et al., “A Tube-and-Droplet-Based Approach for Representing and Analyzing Motion Trajectories,” in IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 39, no. 8, pp. 1489-1503, Aug. 1 2017.DOI: 10.1109/TPAMI.2016.2608884.

Trajectory analysis is essential in many applications. In this paper, we address the problem of representing motion trajectories in a highly informative way, and consequently utilize it for analyzing trajectories. Our approach first leverages the complete information from given trajectories to construct a thermal transfer field which provides a context-rich way to describe the global motion pattern in a scene. Then, a 3D tube is derived which depicts an input trajectory by integrating its surrounding motion patterns contained in the thermal transfer field. The 3D tube effectively: 1) maintains the movement information of a trajectory, 2) embeds the complete contextual motion pattern around a trajectory, 3) visualizes information about a trajectory in a clear and unified way. We further introduce a droplet-based process. It derives a droplet vector from a 3D tube, so as to characterize the high-dimensional 3D tube information in a simple but effective way. Finally, we apply our tube-and-droplet representation to trajectory analysis applications including trajectory clustering, trajectory classification & abnormality detection, and 3D action recognition. Experimental comparisons with state-of-the-art algorithms demonstrate the effectiveness of our approach.

Posted in: Robot motion planning , Tagged:

Several strategies for exploring unknown environments based on graphs extracted from Voronoi diagrams

July 26, 2017 08:30 ,

E. G. Tsardoulias, A. Iliakopoulou, A. Kargakos, L. Petrou, Cost-Based Target Selection Techniques Towards Full Space Exploration and Coverage for USAR applications in a Priori Unknown Environments, J Intell Robot Syst (2017) 87:313–340, DOI: 10.1007/s10846-016-0434-0.

Full coverage and exploration of an environment is essential in robot rescue operations where victim identification is required. Three methods of target selection towards full exploration and coverage of an unknown space oriented for Urban Search and Rescue (USAR) applications have been developed. These are the Selection of the closest topological node, the Selection of the minimum cost topological node and the Selection of the minimum cost sub-graph. All methods employ a topological graph extracted from the Generalized Voronoi Diagram (GVD), in order to select the next best target during exploration. The first method utilizes a distance metric for determining the next best target whereas the Selection of the minimum cost topological node method assigns four different weights on the graph’s nodes, based on certain environmental attributes. The Selection of the minimum cost sub-graph uses a similar technique, but instead of single nodes, sets of graph nodes are examined. In addition, a modification of A* algorithm for biased path creation towards uncovered areas, aiming at a faster spatial coverage, is introduced. The proposed methods’ performance is verified by experiments conducted in two heterogeneous simulated environments. Finally, the results are compared with two common exploration methods.

Posted in: Robot motion planning , Tagged: , ,

Prediction of changes in behaviors of cars for autohomous driving, based on POMDPs made efficient by separation of multiple policies

July 24, 2017 08:50 ,

Enric Galceran, Alexander G. Cunningham, Ryan M. Eustice, Edwin Olson,Multipolicy decision-making for autonomous driving via changepoint-based behavior prediction: Theory and experiment, Autonomous Robots, August 2017, Volume 41, Issue 6, pp 1367–1382, DOI: 10.1007/s10514-017-9619-z.

This paper reports on an integrated inference and decision-making approach for autonomous driving that models vehicle behavior for both our vehicle and nearby vehicles as a discrete set of closed-loop policies. Each policy captures a distinct high-level behavior and intention, such as driving along a lane or turning at an intersection. We first employ Bayesian changepoint detection on the observed history of nearby cars to estimate the distribution over potential policies that each nearby car might be executing. We then sample policy assignments from these distributions to obtain high-likelihood actions for each participating vehicle, and perform closed-loop forward simulation to predict the outcome for each sampled policy assignment. After evaluating these predicted outcomes, we execute the policy with the maximum expected reward value. We validate behavioral prediction and decision-making using simulated and real-world experiments.

Posted in: Robot motion planning , Tagged: , , ,

Reinterpretation of evolutionary processes as algorithms for Bayesian inference

June 30, 2017 11:56 ,

Jordan W. Suchow, David D. Bourgin, Thomas L. Griffiths, Evolution in Mind: Evolutionary Dynamics, Cognitive Processes, and Bayesian Inference, Trends in Cognitive Sciences, Volume 21, Issue 7, July 2017, Pages 522-530, ISSN 1364-6613, DOI: 10.1016/j.tics.2017.04.005.

Evolutionary theory describes the dynamics of population change in settings affected by reproduction, selection, mutation, and drift. In the context of human cognition, evolutionary theory is most often invoked to explain the origins of capacities such as language, metacognition, and spatial reasoning, framing them as functional adaptations to an ancestral environment. However, evolutionary theory is useful for understanding the mind in a second way: as a mathematical framework for describing evolving populations of thoughts, ideas, and memories within a single mind. In fact, deep correspondences exist between the mathematics of evolution and of learning, with perhaps the deepest being an equivalence between certain evolutionary dynamics and Bayesian inference. This equivalence permits reinterpretation of evolutionary processes as algorithms for Bayesian inference and has relevance for understanding diverse cognitive capacities, including memory and creativity.

Posted in: Psycho-physiological bases of engineering , Tagged: ,

A nice general model for camera calibration

June 30, 2017 11:46 ,

S. Ramalingam and P. Sturm, “A Unifying Model for Camera Calibration,” in IEEE Transactions on Pattern Analysis and Machine Intelligence, vol. 39, no. 7, pp. 1309-1319, July 1 2017. DOI: 10.1109/TPAMI.2016.2592904.

This paper proposes a unified theory for calibrating a wide variety of camera models such as pinhole, fisheye, cata-dioptric, and multi-camera networks. We model any camera as a set of image pixels and their associated camera rays in space. Every pixel measures the light traveling along a (half-) ray in 3-space, associated with that pixel. By this definition, calibration simply refers to the computation of the mapping between pixels and the associated 3D rays. Such a mapping can be computed using images of calibration grids, which are objects with known 3D geometry, taken from unknown positions. This general camera model allows to represent non-central cameras; we also consider two special subclasses, namely central and axial cameras. In a central camera, all rays intersect in a single point, whereas the rays are completely arbitrary in a non-central one. Axial cameras are an intermediate case: the camera rays intersect a single line. In this work, we show the theory for calibrating central, axial and non-central models using calibration grids, which can be either three-dimensional or planar.

Posted in: Computer vision , Tagged:

Clock synchronization in a wireless network based on consensus method that takes into account the noise (uncertainty) in the system, with a nice related work about consensus-based network clock synchronization

June 30, 2017 11:37 ,

Jianping He, Xiaoming Duan, Peng Cheng, Ling Shi, Lin Cai, Accurate clock synchronization in wireless sensor networks with bounded noise, Automatica, Volume 81, July 2017, Pages 350-358, ISSN 0005-1098, DOI: 10.1016/j.automatica.2017.03.009.

It is important and challenging to achieve accurate clock synchronization in wireless sensor networks. Various noises, e.g., communication delay, clock fluctuation and measurement errors, are inevitable and difficult to be estimated accurately, which is the main challenge for achieving accurate clock synchronization. In this paper, we focus on how to achieve accurate clock synchronization by considering a practical noise model, bounded noise, which may not satisfy any known distributions. The principle that a bounded monotonic sequence must possess a limit and the concept of maximum consensus are exploited to design a novel clock synchronization algorithm for the network to achieve accurate and fast synchronization. The proposed algorithm is fully distributed, with high synchronization accuracy and fast convergence speed, and is able to compensate both clock skew and offset simultaneously. Meanwhile, we prove that the algorithm converges with probability one, which means that an accurate clock synchronization is achieved. We further prove that the probability of the complete synchronization converges exponentially fast. Experiments and simulations are conducted to verify the noise model and demonstrate the effectiveness of the proposed algorithm.

Posted in: Communication networks , Tagged:

A good intro about actor-critic and decision making without model on MDPs

June 30, 2017 11:31 ,

J. Wang and I. C. Paschalidis, “An Actor-Critic Algorithm With Second-Order Actor and Critic,” in IEEE Transactions on Automatic Control, vol. 62, no. 6, pp. 2689-2703, June 2017.DOI: 10.1109/TAC.2016.2616384.

Actor-critic algorithms solve dynamic decision making problems by optimizing a performance metric of interest over a user-specified parametric class of policies. They employ a combination of an actor, making policy improvement steps, and a critic, computing policy improvement directions. Many existing algorithms use a steepest ascent method to improve the policy, which is known to suffer from slow convergence for ill-conditioned problems. In this paper, we first develop an estimate of the (Hessian) matrix containing the second derivatives of the performance metric with respect to policy parameters. Using this estimate, we introduce a new second-order policy improvement method and couple it with a critic using a second-order learning method. We establish almost sure convergence of the new method to a neighborhood of a policy parameter stationary point. We compare the new algorithm with some existing algorithms in two applications and demonstrate that it leads to significantly faster convergence.

Posted in: Artificial Intelligence , Tagged: , ,

Interesting review of approaches to visually detect loop closings in robotics, and a novel, very efficient method that is independent on the image representation and based on not using the typical l2 norm (least squares), which leads to dense optimization problems

June 30, 2017 11:10 ,

Yasir Latif, Guoquan Huang, John Leonard, José Neira, Sparse optimization for robust and efficient loop closing, Robotics and Autonomous Systems, Volume 93, July 2017, Pages 13-26, ISSN 0921-8890,DOI: 10.1016/j.robot.2017.03.016.

It is essential for a robot to be able to detect revisits or loop closures for long-term visual navigation. A key insight explored in this work is that the loop-closing event inherently occurs sparsely, i.e., the image currently being taken matches with only a small subset (if any) of previous images. Based on this observation, we formulate the problem of loop-closure detection as a sparse, convex
ℓ 1 -minimization problem. By leveraging fast convex optimization techniques, we are able to efficiently find loop closures, thus enabling real-time robot navigation. This novel formulation requires no offline dictionary learning, as required by most existing approaches, and thus allows online incremental operation. Our approach ensures a unique hypothesis by choosing only a single globally optimal match when making a loop-closure decision. Furthermore, the proposed formulation enjoys a flexible representation with no restriction imposed on how images should be represented, while requiring only that the representations are “close” to each other when the corresponding images are visually similar. The proposed algorithm is validated extensively using real-world datasets.

Posted in: Mobile robot mapping, Mobile robot SLAM , Tagged: