Efficient Visual SLAM for Autonomous Aerial Vehicles

The general interest in autonomous or semi-autonomous micro aerial vehicles (MAVs) is strongly increasing. There are already several commercial applications for autonomous micro aerial vehicles and many more being investigated by both research institutes and multiple financially strong companies. Most commercially available applications, however, are rather limited in their autonomy: They rely either on a human operator or reliable reception of global positioning system (GPS) signals for navigation. Truly autonomous micro aerial vehicles that can also fly in GPS-denied environments such as indoors, in forests, or in urban scenarios, where the GPS signal may be blocked by tall buildings, clearly require more on-board sensing and computation potential. In this dissertation, we explore autonomous micro aerial vehicles that rely on a so-called RGBD camera as their main sensor for simultaneous localization and mapping (SLAM). Several aspects of efficient visual SLAM with RGBD cameras aimed at micro aerial vehicles are studied in detail within this dissertation: We first propose a novel principle of integrating depth measurements within visual SLAM systems by combining both 2D image position and depth measurements. We modify a widely-used visual odometry system accordingly, such that it can serve as a robust and accurate odometry system for RGBD cameras. Based on this principle we go on and implement a full RGBD SLAM system that can close loops and perform global pose graph optimization and runs in real-time on the computationally constrained onboard computer of our MAV. We investigate the feasibility of explicitly detecting loops using depth images as opposed to intensity images with a state of the art hierarchical bag of words (BoW) approach using depth image features. Since an MAV flying indoors can often see a clearly distinguishable ground plane, we develop a novel efficient and accurate ground plane detection method and show how to use this to suppress drift in height and attitude. Finally, we create a full SLAM system combining the earlier ideas that enables our MAV to fly autonomously in previously unknown environments while creating a map of its surroundings

Towards Visual Ego-motion Learning in Robots

Many model-based Visual Odometry (VO) algorithms have been proposed in the past decade, often restricted to the type of camera optics, or the underlying motion manifold observed. We envision robots to be able to learn and perform these tasks, in a minimally supervised setting, as they gain more experience. To this end, we propose a fully trainable solution to visual ego-motion estimation for varied camera optics. We propose a visual ego-motion learning architecture that maps observed optical flow vectors to an ego-motion density estimate via a Mixture Density Network (MDN). By modeling the architecture as a Conditional Variational Autoencoder (C-VAE), our model is able to provide introspective reasoning and prediction for ego-motion induced scene-flow. Additionally, our proposed model is especially amenable to bootstrapped ego-motion learning in robots where the supervision in ego-motion estimation for a particular camera sensor can be obtained from standard navigation-based sensor fusion strategies (GPS/INS and wheel-odometry fusion). Through experiments, we show the utility of our proposed approach in enabling the concept of self-supervised learning for visual ego-motion estimation in autonomous robots.Comment: Conference paper; Submitted to IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS) 2017, Vancouver CA; 8 pages, 8 figures, 2 table

Learning Pose Estimation for UAV Autonomous Navigation and Landing Using Visual-Inertial Sensor Data

In this work, we propose a robust network-in-the-loop control system for autonomous navigation and landing of an Unmanned-Aerial-Vehicle (UAV). To estimate the UAV’s absolute pose, we develop a deep neural network (DNN) architecture for visual-inertial odometry, which provides a robust alternative to traditional methods. We first evaluate the accuracy of the estimation by comparing the prediction of our model to traditional visual-inertial approaches on the publicly available EuRoC MAV dataset. The results indicate a clear improvement in the accuracy of the pose estimation up to 25% over the baseline. Finally, we integrate the data-driven estimator in the closed-loop flight control system of Airsim, a simulator available as a plugin for Unreal Engine, and we provide simulation results for autonomous navigation and landing