Publications
JOURNAL PUBLICATIONS
L.-H. Nguyen, M.-D. Hua, G. Allibert, T. Hamel. A homography-based dynamic control approach applied to station keeping of autonomous underwater vehicles without linear velocity measurements. In IEEE Transactions on Control Systems Technology, 29 (5), 2065-2078, 2021.
Abstract: A homography-based dynamic control approach applied to station keeping of Autonomous Underwater Vehicles (AUVs) without relying on linear velocity measurements is proposed. The homography estimated from images of a planar target scene captured by a downward-looking camera is directly used as feedback information. The full dynamics of the AUV are exploited in a hierarchical control design with inner-outer loop architecture. Enhanced by integral compensation actions and disturbance torque estimation, the proposed controller is robust with respect to model uncertainties and unknown currents. The performance of the proposed control approach is illustrated via both comparative simulation results conducted on a realistic AUV model and experimental validations on an in-house AUV.
Demo videos: view here
S. de Marco, M.-D. Hua, T. Hamel, R. Mahony (2021). Homography Estimation of a Moving Planar Scene from Direct Point Correspondence. In IEEE Transactions on Control Systems Technology, 29 (3), 1284-1295, 2021.
Abstract: Homography estimation is an important task in robotics applications such as landing on moving platforms, docking and refueling, building inspection, etc. Non-linear observers depend on an estimate of the group algebra velocity as a feed-forward term to minimize lag in the filter response. When both the camera and the scene are moving, and for perspective image constructs such as the homography, it is often impossible to directly measure the required group velocity. This paper proposes a solution for the case where the motion is periodic, or approximately periodic, with known period. The approach is based on the internal model principle, where the internal model can be expanded to include a sufficient harmonics of the desired period in order to model complex periodic motions. The novelty of the work lies in formalizing the internal model for observer design to the non-compact Lie group SL(3) and providing a demonstration of the effectiveness of the approach with real-world examples.
M.-D. Hua, J. Trumpf, T. Hamel, R. Mahony, P. Morin. Nonlinear observer design on SL(3) for homography estimation by exploiting point and line correspondences with application to image stabilization. In Automatica, 115, 108858, 2020.
Abstract: Although homography estimation from correspondences of mixed-type features, namely points and lines, has been relatively well studied with algebraic approaches by the computer vision community, this problem has never been addressed with nonlinear observer paradigms. In this paper, a novel nonlinear observer on the Special Linear group SL(3) applied to homography estimation is developed. The key advance with respect to similar works on the topic is the formulation of observer innovation that exploits directly point and line correspondences as input without requiring prior algebraic reconstruction of individual homographies. Rigourous observability and stability analysis is provided. A potential application to image stabilization in presence of very fast camera motion, severe occlusion, specular reflection, image blur, and light saturation is demonstrated with very encouraging results.
CONFERENCE PUBLICATIONS
P. Gintrand, M.-D. Hua, , T. Hamel, G. Varra (2023). A novel observer design for monocular Visual SLAM. Submitted in November 2022 to IFAC World Congress 2023.
Abstract: A novel cascaded observer design exploiting source points' bearing measurements is proposed for the monocular visual SLAM (Simultaneous Localization And Mapping) problem. A distinguishing feature of the present work with respect to most existing visual SLAM algorithms is the decoupling of the camera's pose estimation (i.e., localization) from source points' position estimation (i.e., map building), leading to a straightforward architecture that can handle a vast number of source points efficiently and that does not jeopardize the use of robustification techniques for the search of source point correspondences in images (e.g., RANSAC). Furthermore, the persistence of excitation of the camera's translational motion together with the source points' configuration (specified in our prior works) is the key to achieving (local) exponential stability of the camera's pose estimation and, subsequently, overcoming the wellknown depth ambiguity associated with the use of a monocular camera. This ingredient has paved the way for the proposed cascaded observer architecture, in which the main contributions concern the design and stability analysis of the three proposed observers for source points' position estimation. Convincing comparative simulation and experimental results are reported to support the proposed approach.
T. Bouazza, T. Hamel, M.-D. Hua, R. Mahony (2022). Homography-based Riccati observer design for camera pose estimation. To appear in 61st IEEE Conference on Decision and Control, 2022.
Abstract: This paper introduces a novel approach for estimating the relative pose of a mobile robot equipped with an onboard IMU, a velocity sensor complemented with a monocular camera observing a planar scene. The proposed solution relies on the design of a deterministic Riccati observer that exploits the first-order approximations of a class of nonlinear systems. It uses the point-feature correspondences of a sequence of images and exploits the homography constraint to derive the system's measurement equation. The observability analysis, which highlights the uniform observability condition under which local exponential stability is guaranteed, is performed. Moreover, an extension of the observer to depth estimation is provided. Finally, the proposed observer solution is validated through simulation and experimental results.
P. Gintrand, M.-D. Hua, T. Hamel, G. Varra (2022). On the uniform observability of the relative pose estimation problem using bearing measurements and epipolar constraints. To appear in 61st IEEE Conference on Decision and Control, 2022.
Abstract: This paper proposes a comprehensive observability analysis of the relative pose estimation of a monocular camera (moving in three-dimensional space) from bearing measurements and epipolar constraints. It extends our previous work on observer design for the particular case of 3-source points with unknown 3D coordinates. The paper addresses the observability analysis of the more general case of n-source points (n ≥ 3) using persistence of excitation of the translational motion and bearing references (or equivalently, the position of the origin of the reference frame with respect to the source points). The key contribution of this work is to show that the persistence of excitation is not enough to guarantee uniform observability. In particular, we show that uniform observability also depends on bearing references and the number of observed source points.
M.-D. Hua, S. de Marco, T. Hamel, R. Beard (2020). Relative pose estimation from bearing measurements of three unknown source points. In proceedings of IEEE Conference on Decision and Control (CDC), pp. 4176-4181, 2020.
Abstract: This paper unveils a novel discovery that the full relative pose of a monocular camera moving in a three dimensional space can be estimated exploiting bearing measurements of only 3 unknown source points (together with velocity measurements) without any additional knowledge if the camera translational motion is sufficiently exciting. The epipolar constraint commonly used in Computer Vision algebraic algorithms for the determination of the so-called essential matrix (all of them require at least 5 source points) is here exploited in the design of the proposed Riccati observer for pose estimation. One remarkable feature of this work is the determination of an explicit persistence of excitation condition that guarantees uniform observability and, subsequently, (local) exponential stability of the proposed observer. Convincing simulation results are provided to support the proposed approach.
S. de Marco, M.-D. Hua, T. Hamel, C. Samson (2020). Position, Velocity, Attitude and Accelerometer-Bias Estimation from IMU and Bearing Measurements. In proceedings of European Control Conference (ECC'20), pp. 1003-1008, 2020.
Abstract: This paper considers the problem of estimating the position, attitude and velocity of a rigid-body in a 3D space by fusing bearing measurements provided by a monocular camera with gyroscopic and accelerometer measurements provided by an Inertial Measurement Unit (IMU). The proposed deterministic observer is accompanied with an observability analysis, that points out the minimum number of image points (bearings) along with their configuration in the inertial frame, under which local exponential stability is guaranteed. The performance of the observer is demonstrated by performing experiments on a test-bed inertial-Visual sensor.
Riccati observer design for homography decomposition. In proceedings of European Control Conference (ECC'20), pp. 1306-1311, 2020.
Abstract: The paper addresses the challenging problem of image-based dynamic control of Autonomous Underwater Vehicles observing a (near) vertical planar target, without measuring the linear velocity. The proposed control approach exploits a minimum sensor suite consisting of a camera looking forward to provide images from which the homography matrix is extracted and an IMU providing angular velocity and gravity direction measurements. The dynamics of the AUV are exploited in a hierarchical control scheme with inner-outer control loop architecture. Rigourous stability analysis is established. The performance of the proposed approach is illustrated via simulation results conducted on a realistic AUV model.
L.-H. Nguyen, M.-D. Hua, T. Hamel (2019). A nonlinear control approach for trajectory tracking of slender-body axisymmetric underactuated underwater vehicles. In proceedings of European Control Conference (ECC'19), pp. 4053-4060, 2019, Invited Paper.
Abstract: This paper develops a novel nonlinear control approach for slender-body underactuated underwater vehicles with a body shape symmetric with respect to the longitudinal axis. Compared to aerial vehicles, added-mass effects are much more preponderant and complex for underwater vehicles, especially for slender bodies. By considering an axisymmetric body, these added-mass effects along with dissipative hydrodynamic force are carefully taken into account via various adaptations and decompositions, resulting in a modified “apparent” force independent of the vehicle’s orientation and subsequently a nonlinear system with a triangular control structure. The proposed controller is then complemented with an integral correction term so as to enhance its robustness with respect to model uncertainties and external disturbances. Comparative simulation results conducted on a realistic model of a quasi axisymmetric underwater vehicle illustrate the performance and robustness of the proposed control approach.