Optimal Image-Aided Inertial Navigation

The utilization of cameras in integrated navigation systems is among the most recent scientific research and high-tech industry development. The research is motivated by the requirement of calibrating off-the-shelf cameras and the fusion of imaging and inertial sensors in poor GNSS environments. The three major contributions of this dissertation are The development of a structureless camera auto-calibration and system calibration algorithm for a GNSS, IMU and stereo camera system. The auto-calibration bundle adjustment utilizes the scale restraint equation, which is free of object coordinates. The number of parameters to be estimated is significantly reduced in comparison with the ones in a self-calibrating bundle adjustment based on the collinearity equations. Therefore, the proposed method is computationally more efficient. The development of a loosely-coupled visual odometry aided inertial navigation algorithm. The fusion of the two sensors is usually performed using a Kalman filter. The pose changes are pairwise time-correlated, i.e. the measurement noise vector at the current epoch is only correlated with the one from the previous epoch. Time-correlated errors are usually modelled by a shaping filter. The shaping filter developed in this dissertation uses Cholesky factors as coefficients derived from the variance and covariance matrices of the measurement noise vectors. Test results with showed that the proposed algorithm performs better than the existing ones and provides more realistic covariance estimates. The development of a tightly-coupled stereo multi-frame aided inertial navigation algorithm for reducing position and orientation drifts. Usually, the image aiding based on the visual odometry uses the tracked features only from a pair of the consecutive image frames. The proposed method integrates the features tracked from multiple overlapped image frames for reducing the position and orientation drifts. The measurement equation is derived from SLAM measurement equation system where the landmark positions in SLAM are algebraically by time-differencing. However, the derived measurements are time-correlated. Through a sequential de-correlation, the Kalman filter measurement update can be performed sequentially and optimally. The main advantages of the proposed algorithm are the reduction of computational requirements when compared to SLAM and a seamless integration into an existing GNSS aided-IMU system

Des cartes combinatoires pour la construction automatique de modèles d'environnement par un robot mobile

Ce travail s'inscrit dans la problématique classique de localisation et de cartographie simultanées pour un robot mobile évoluant en milieu intérieur supposé inconnu. Son originalité réside dans la définition d'un modèle de carte très structuré fondé sur un outil algébrique appelé « carte combinatoire », qui combine plusieurs types de représentations géométriques (modèles surfaciques et cartes basées sur des primitives géométriques) et fournit des informations topologiques telles que les liens d'adjacence. Nous détaillons la chaîne algorithmique permettant de construire des cartes en ligne suivant ce modèle, avec un robot équipé d'un télémètre laser à balayage : il s'agit d'adapter les techniques habituelles basées sur le filtrage de Kalman afin de gérer les relations d'adjacence (appariement de chaînes polygonales, définition de points de cassure virtuels, mises à jour géométrique et topologique spécifiques). Des résultats expérimentaux illustrent et valident les divers mécanismes mis en oeuvre. ABSTRACT : This thesis focuses on the well-known Simultaneous Localization And Map-building (SLAM) problem for indoor mobile robots. The novelty of this work lies in the definition of a well-structured map model based on an algebraic tool called « combinatorial map » which combines different kinds of geometric representations (space-based, grid-based as well as feature-based formats) and provides topological information such as adjacency links between map elements. We describe the whole algorithm designed to build maps on line according to this model, using a robot equipped with a laser scanner. Classical techniques relying on Kalman filtering are adapted in order to deal with adjacency relationships (via polyline matching, the use of virtual break-points and specific geometric and topological update operations). Exeprimental results are presented to illustrate and validate the various mecanisms involved in this process