Showing papers by "Ivan Petrović published in 2016"

Full body human motion estimation on lie groups using 3D marker position measurements

Abstract: This paper proposes a new algorithm for full body human motion estimation using 3D marker position measurements. The joints are represented with Lie group members, including special orthogonal groups SO(2) and SO(3), and a special euclidean group SE(3). We employ the Lie Group Extended Kalman Filter (LG-EKF) for stochastic inference on groups, thus explicitly accounting for the non-euclidean geometry of the state space, and provide the derivation of the LG-EKF recursion for articulated motion estimation. We evaluate the performance of the proposed algorithm in both simulation and on real-world motion capture data, comparing it with the Euler angles based EKF. The results show that the proposed filter significantly outperforms the Euler angles based EKF, since it estimates human motion more accurately and is not affected by gimbal lock.

Detailed octorotor modeling and PD control

Abstract: This paper presents a detailed octorotor model derivation. The full derivation of the rigid octorotor body dynamics based on the Newton-Euler approach including the Gyroscopic effect and motor dynamics is given. We also discuss a generalization of the model thus making it applicable to any symmetric and balanced multirotor aerial vehicle (MAV) system with even number of rotors. Finally, simple stabilization control is designed and compared with the state of the art results.

Moving object tracking employing rigid body motion on matrix Lie groups

Abstract: In this paper we propose a novel method for estimating rigid body motion by modeling the object state directly in the space of the rigid body motion group SE(2). It has been recently observed that a noisy manoeuvring object in SE(2) exhibits banana-shaped probability density contours in its pose. For this reason, we propose and investigate two state space models for moving object tracking: (i) a direct product SE(2) × ℝ3 and (ii) a direct product of the two rigid body motion groups SE(2) × SE(2). The first term within these two state space constructions describes the current pose of the rigid body, while the second one employs its second order dynamics, i.e., the velocities. By this, we gain the flexibility of tracking omnidirectional motion in the vein of a constant velocity model, but also accounting for the dynamics in the rotation component. Since the SE(2) group is a matrix Lie group, we solve this problem by using the extended Kalman filter on matrix Lie groups and provide a detailed derivation of the proposed filters. We analyze the performance of the filters on a large number of synthetic trajectories and compare them with (i) the extended Kalman filter based constant velocity and turn rate model and (ii) the linear Kalman filter based constant velocity model. The results show that the proposed filters outperform the other two filters on a wide spectrum of types of motion.

Appearance Based Vehicle Detection by Radar-Stereo Vision Integration

Abstract: This paper proposes a novel method for appearance based vehicle detection by employing stereo vision system and radar units. In the vein of utilizing advanced driver assistance systems, detection and tracking of moving objects or particularly vehicles, represents an essential task. For the merits of such application, it has often been suggested to combine multiple sensors with complementary modalities. In accordance, in this work we utilize a stereo vision and two radar units, and fuse the corresponding modalities at the level of detection. Firstly, the algorithm executes the detection procedure based on stereo image solely, generating the information about vehicles’ position. Secondly, the final unique list of vehicles is obtained by overlapping the radar readings with the preliminary list obtained by stereo system. The stereo vision–based detection procedure consists of (i) edge processing plugging in also the information about disparity map, (ii) shape based vehicles’ contour extraction and (iii) preliminary vehicles’ positions generation. Since the radar readings are examined by overlapping them with the list obtained by stereo vision, the proposed algorithm can be considered as high level fusion approach. We analyze the performance of the proposed algorithm by performing the real-world experiment in highly dynamic urban environment, under significant illumination influences caused by sunny weather.

Fast Active SLAM for Accurate and Complete Coverage Mapping of Unknown Environments

Abstract: In this paper, we present an active SLAM solution with an active loop closing component which is independent on exploration component and at the same time allows high accuracy robot’s pose estimation and complete environment mapping. Inputs to our SLAM algorithm are RGBD image from the Kinect sensor and odometry estimates obtained from inertial measurement unit and wheel encoders. SLAM is based on the exactly sparse delayed state filter for real-time estimation of robot’s trajectory, vision-based pose registration, and loop closing. The active component ensures that localization remains accurate over a long period of time by sending the robot to close loops if a criterion function satisfies the predefined value. Our criterion function depends on the number of states predicted without an update between predictions, information gained from loop closing and the sheer distance between the loop closing state location and the current robot location. Once a state in which a loop closure should occur is reached and an update is performed, the robot returns to its previous goals. Since the active component is independent on the exploration part, the SLAM solution described in this paper can easily be merged with any existing exploration algorithm and the only requirement is that the exploration algorithm is able to stop exploration at any time and continue the exploration after the loop closing was accomplished. In this paper, we propose an active SLAM integration with the 2D laser range finder-based exploration algorithm that ensures the complete coverage of a polygonal environment and therefore a detailed mapping. The developed Active SLAM solution was verified through experiments which demonstrated its capability to work in real-time and to consistently map polygonal environments.

Multitarget tracking with the von Mises-Fisher filter and probabilistic data association

Abstract: Directional data emerge in many scientific disciplines due to the nature of the observed phenomena or the working principles of a sensor. The problem of tracking with direction- only sensors is challenging since the motion of the target typically resides either in 3D or 2D Euclidean space, while the corresponding measurements reside either on the unit sphere or the unit circle, respectively. Furthermore, in multitarget tracking there is the need to deal with the problem of pairing sensors measurements with targets in the presence of clutter (the data association problem). In this paper we propose to approach multitarget tracking in clutter with direction-only data by setting it on the unit hypersphere, thus tracking the objects with a Bayesian estimator based on the von Mises-Fisher distribution and probabilistic data association. To achieve this goal we derive the probabilistic data association (PDA) filter and the joint probabilistic data association (JPDA) filter for the Bayesian von Mises-Fisher estimation on the unit hypersphere. The final PDA and JPDA filter equations are derived with respect to the Kullback-Leibler divergence by preserving the first moment of the hyperspherical distribution. Although the fundamental equations are given for the hyperspherical case, we focus on the filters on the unit 1- sphere (circle in R^2) and the unit 2-sphere (surface of the unit ball in R^3). The proposed approach is validated through synthetic data experiments on 100 Monte Carlo runs simulating multitarget tracking with noisy directional measurements and clutter.

On wrapping the Kalman filter and estimating with the SO(2) group

Abstract: This paper analyzes directional tracking in 2D with the extended Kalman filter on Lie groups (LG-EKF). The study stems from the problem of tracking objects moving in 2D Euclidean space, with the observer measuring direction only, thus rendering the measurement space and object position on the circle—a non-Euclidean geometry. The problem is further inconvenienced if we need to include higher-order dynamics in the state space, like angular velocity which is a Euclidean variables. The LG-EKF offers a solution to this issue by modeling the state space as a Lie group or combination thereof, e.g., SO(2) or its combinations with ℝn. In the present paper, we first derive the LG-EKF on SO(2) and subsequently show that this derivation, based on the mathematically grounded framework of filtering on Lie groups, yields the same result as heuristically wrapping the angular variable within the EKF framework. This result applies only to the SO(2) and SO(2) × ℝn LG-EKFs and is not intended to be extended to other Lie groups or combinations thereof. In the end, we showcase the SO(2) × ℝ2 LG-EKF, as an example of a constant angular acceleration model, on the problem of speaker tracking with a microphone array for which real-world experiments are conducted and accuracy is evaluated with ground truth data obtained by a motion capture system.

Robot arm teleoperation via RGBD sensor palm tracking

Abstract: In this paper we present a simple and intuitive approach to teleoperating a 3 or higher degrees-of-freedom (DOF) robotic arm in Cartesian space. Using an RGBD camera, we retrieve the position of the user's palm. This position is then translated into the desired robotic arm position, which is then used as an input to a control loop. The entire system is implemented in the Robotic Operating System, enabling simple functionality transfer to any compatible robotic arm. The system was tested on the Kinova Jaco 6DOF robotic arm with the aim of using it for object manipulation. We use the inverse kinematics for calculating the joint rotation velocities required for following the Cartesian path of the human hand. The resulting joint velocities are then sent to the robotic arm control interface which then passes commands to the pertaining API. Results corroborate the validity of the proposed approach for robotic arm teleoperation, opening the possibility for many potential applications.

Moving Objects Tracking on the Unit Sphere Using a Multiple-Camera System on a Mobile Robot

Abstract: Detection and tracking of moving objects with camera systems mounted on a mobile robot presents a formidable problem since the ego-motion of the robot and the moving objects jointly form a challengingly discernible motion in the image. In this paper, we are concerned with multiple-camera systems, namely the Ladybug\(^{\textregistered }2\) camera, whose perspective images were used to detect motion and subsequently perform the tracking of multiple objects on the sphere. This enabled us to account for the continuity of the scene which is achieved by the sensor in an image stitching process on the sphere. The objects are tracked on the sphere with a Bayesian filter based on the von Mises–Fisher distribution and the data association is achieved by the global nearest neighbor method, for which the distance matrix is constructed by deriving the Renyi \(\alpha \)-divergence for the von Mises–Fisher distribution. The prospects of the method are tested on a synthetic and real-world data experiments.

Short-Term Map Based Detection and Tracking of Moving Objects with 3D Laser on a Vehicle

Abstract: Detection and tracking of moving objects is an essential problem in situational awareness context and hence crucial for many robotic applications. Here we propose a method for the detection of moving objects with a 3D laser range sensor and a variation of the method for tracking multiple detected objects. The detection procedure starts with the ground extraction using random sample consensus approach for model parameter estimation. The resulting point cloud is then downsampled using voxel grid approach and filtered using a radius outlier rejection method. Within the approach, we have utilized a procedure for building short-term maps of the environment by using the octree data structure. This data structure enables an efficient comparison of the current scan and the short-term local map, thus detecting dynamic parts of scene. The ego-motion of the mobile platform is compensated using the available odometry information, which is rather imperfect, and hence is refined using the iterative closest point registration technique. Furthermore, due to sensor characteristics, the iterative closest point is carried out in 2D between the short-term map and the current, where the non-ground filtered scans are projected onto 2D. The tracking task is based on the joint probabilistic data association filter and Kalman filtering with variable process and measurement noise which take into account velocity and position of the tracked objects. Since this data association approach assumes a constant and known number of objects, we have utilized a specific entropy based track management. The experiments performed using Velodyne HDL-32E laser sensor mounted on top of a mobile platform demonstrate the suitability and efficiency of the proposed method.