A Multi-Sensor Navigation System for Outdoor and Indoor Environments

Abstract

A navigation system for quadrotor helicopters operating in outdoor and indoor environments is presented in this paper. The vehicle is equipped with an inertial measurement unit (IMU), a Global Positioning System (GPS) receiver, a digital compass, an air pressure sensor, and a 2D laser rangefinder. While accurate navigation solutions can be obtained for outdoor or indoor environments with state-of-the-art approaches, it is important to maintain good performance during outdoor-indoor and indooroutdoor transitions as well as urban canyon scenarios. The navigation system presented in this paper uses absolute GPS position and velocity measurements and relative measurements calculated from laser rangefinder scans simultaneously. Filter state augmentation is used to compensate for delays and to process relative measurements. A filter status is introduced based on the classification of GPS position measurements. This filter status is used to determine the necessity of processing relative measurements. Thus, for example, it can be avoided to process relative measurements in outdoor open sky conditions where GPS measurements are sufficient for good filter performance. The accuracy and robustness of the approach is demonstrated with three trajectories, each covering open sky areas, sections with high buildings and poor GPS signal reception, and transitions into buildings. Despite the challenging environments an accurate and consistent navigation solution is achieved and a seamless integration of absolute and relative measurements is accomplished.