Gian Diego Tipaldi

People tracking with human motion predictions from social forces

For many tasks in populated environments, robots need to keep track of current and future motion states of people. Most approaches to people tracking make weak assumptions on human motion such as constant velocity or acceleration. But even over a short period, human behavior is more complex and influenced by factors such as the intended goal, other people, objects in the environment, and social rules. This motivates the use of more sophisticated motion models for people tracking especially since humans frequently undergo lengthy occlusion events. In this paper, we consider computational models developed in the cognitive and social science communities that describe individual and collective pedestrian dynamics for tasks such as crowd behavior analysis. In particular, we integrate a model based on a social force concept into a multi-hypothesis target tracker. We show how the refined motion predictions translate into more informed probability distributions over hypotheses and finally into a more robust tracking behavior and better occlusion handling. In experiments in indoor and outdoor environments with data from a laser range finder, the social force model leads to more accurate tracking with up to two times fewer data association errors.

Fast and accurate SLAM with Rao–Blackwellized particle filters

Rao-Blackwellized particle filters have become a popular tool to solve the simultaneous localization and mapping problem. This technique applies a particle filter in which each particle carries an individual map of the environment. Accordingly, a key issue is to reduce the number of particles and/or to make use of compact map representations. This paper presents an approximative but highly efficient approach to mapping with Rao-Blackwellized particle filters. Moreover, it provides a compact map model. A key advantage is that the individual particles can share large parts of the model of the environment. Furthermore, they are able to reuse an already computed proposal distribution. Both techniques substantially speed up the overall filtering process and reduce the memory requirements. Experimental results obtained with mobile robots in large-scale indoor environments and based on published standard datasets illustrate the advantages of our methods over previous mapping approaches using Rao-Blackwellized particle filters.

Robust map optimization using dynamic covariance scaling

Developing the perfect SLAM front-end that produces graphs which are free of outliers is generally impossible due to perceptual aliasing. Therefore, optimization back-ends need to be able to deal with outliers resulting from an imperfect front-end. In this paper, we introduce dynamic covariance scaling, a novel approach for effective optimization of constraint networks under the presence of outliers. The key idea is to use a robust function that generalizes classical gating and dynamically rejects outliers without compromising convergence speed. We implemented and thoroughly evaluated our method on publicly available datasets. Compared to recently published state-of-the-art methods, we obtain a substantial speed up without increasing the number of variables in the optimization process. Our method can be easily integrated in almost any SLAM back-end.

FLIRT - Interest regions for 2D range data

Local image features are used for a wide range of applications in computer vision and range imaging. While there is a great variety of detector-descriptor combinations for image data and 3D point clouds, there is no general method readily available for 2D range data. For this reason, the paper first proposes a set of benchmark experiments on detector repeatability and descriptor matching performance using known indoor and outdoor data sets for robot navigation. Secondly, the paper introduces FLIRT that stands for Fast Laser Interest Region Transform, a multi-scale interest region operator for 2D range data. FLIRT combines the best detector with the best descriptor, experimentally found in a comprehensive analysis of alternative detector and descriptor approaches. The analysis yields repeatability and matching performance results similar to the values found for features in the computer vision literature, encouraging a wide range of applications of FLIRT on 2D range data. We finally show how FLIRT can be used in conjunction with RANSAC to address the loop closing/global localization problem in SLAM in indoor as well as outdoor environments. The results demonstrate that FLIRT features have a great potential for robot navigation in terms of precision-recall performance, efficiency and generality.

On the position accuracy of mobile robot localization based on particle filters combined with scan matching

Many applications in mobile robotics and especially industrial applications require that the robot has a precise estimate about its pose. In this paper, we analyze the accuracy of an integrated laser-based robot pose estimation and positioning system for mobile platforms. For our analysis, we used a highly accurate motion capture system to precisely determine the error in the robots pose. We are able to show that by combining standard components such as Monte-Carlo localization, KLD sampling, and scan matching, an accuracy of a few millimeters at taught-in reference locations can be achieved. We believe that this is an important analysis for developers of robotic applications in which pose accuracy matters.

Place-dependent people tracking

People detection and tracking are important in many situations where robots and humans work and live together. But unlike targets in traditional tracking problems, people typically move and act under the constraints of their environment. The probabilities and frequencies for when people appear, disappear, walk or stand are not uniform but vary over space making human behavior strongly place-dependent. In this paper we present a model that encodes spatial priors on human behavior and show how the model can be incorporated into a people-tracking system. We learn a non-homogeneous spatial Poisson process that improves data association in a multi-hypothesis target tracker through more informed probability distributions over hypotheses. We further present a place-dependent motion model whose predictions follow the space-usage patterns that people take and which are described by the learned spatial Poisson process. Large-scale experiments in different indoor and outdoor environments using laser range data, demonstrate how both extensions lead to more accurate tracking behavior in terms of data-association errors and number of track losses. The extended tracker is also slightly more efficient than the baseline approach. The system runs in real-time on a typical desktop computer.

Lifelong localization in changing environments

Robot localization systems typically assume that the environment is static, ignoring the dynamics inherent in most real-world settings. Corresponding scenarios include households, offices, warehouses and parking lots, where the location of certain objects such as goods, furniture or cars can change over time. These changes typically lead to inconsistent observations with respect to previously learned maps and thus decrease the localization accuracy or even prevent the robot from globally localizing itself. In this paper we present a sound probabilistic approach to lifelong localization in changing environments using a combination of a Rao-Blackwellized particle filter with a hidden Markov model. By exploiting several properties of this model, we obtain a highly efficient map management approach for dynamic environments, which makes it feasible to run our algorithm online. Extensive experiments with a real robot in a dynamically changing environment demonstrate that our algorithm reliably adapts to changes in the environment and also outperforms the popular Monte-Carlo localization approach.

Cooperative robot localization and target tracking based on least squares minimization

In this paper we address the problem of cooperative localization and target tracking with a team of moving robots. We model the problem as a least squares minimization problem and show that this problem can be efficiently solved using sparse optimization methods. To achieve this, we represent the problem as a graph, where the nodes are robot and target poses at individual time-steps and the edges are their relative measurements. Static landmarks at known position are used to define a common reference frame for the robots and the targets. In this way, we mitigate the risk of using measurements and state estimates more than once, since all the relative measurements are i.i.d. and no marginalization is performed. Experiments performed using a set of real robots show higher accuracy compared to a Kalman filter.

Nonlinear Graph Sparsification for SLAM

In this paper we present a novel framework for nonlinear graph sparsification in the context of simultaneous localization and mapping. Our approach is formulated as a convex minimization problem, where we select the set of nonlinear measurements that best approximate the original distribution. In contrast to previous algorithms, our method does not require a global linearization point and can be used with any nonlinear measurement function. Experiments performed on several publicly available datasets demonstrate that our method outperforms the state of the art with respect to the KullbackLeibler divergence and the sparsity of the solution.

I want my coffee hot! Learning to find people under spatio-temporal constraints

In this paper we present a probabilistic model for spatio-temporal patterns of human activities that enable robots to blend themselves into the work-flows and daily routines of people. The model, called spatial affordance map, is a non-homogeneous spatial Poisson process that relates space, time and occurrence probability of activity events. We describe how learning and inference is made and present a novel planning algorithm that produces paths which maximize the probability to encounter a person. We show that the problem is a special class of the orienteering problem that can be solved as a finite horizon Markov decision process. We develop a simulator of populated office environments to validate the model and the planning algorithm. The simulated agents follow activity patterns learned by administering a questionnaire to 27 colleagues over two weeks. The experiments shows that the model is statistically valid with respect to both the Anderson-Darling test and the expected waiting time estimation. They further show that the proposed algorithm is able to find optimal paths.