Camera-Lidar Navigation for Large Unmanned Aircraft: Modular System Design and Safe Closed-Loop Testing Methodology

This paper presents an optical navigation method for unmanned flights where satellite navigation might be disturbed. Core is an inertial-based navigation filter that provides high-frequent flight state updates and where satellite positioning can be replaced with updates from optical sensors in case of satellite signal dropouts. This alternative positioning is determined by a simultaneous localization and mapping (SLAM) algorithm that can generally handle 2D and 3D feature inputs from arbitrary sources. In the presented setup, 2D features are generated from camera images where 3D information from laser range is added if available. Within a simulation environment, visual SLAM is fed with emulated inputs. The architecture provides strong separation, i.e. the sensor pre-processing, visual SLAM, state estimation, and flight control modules are exchangeable and can be run and tested independently. This concept may prevent a very tight coupling of all components, but with regard to future certification, validation and verification will be easier once single components are assured. The navigation method is tested in two ways: first within a flight test of an 85-kg helicopter where only the quality of optical-aided state estimation is tested, and second within a closed-loop simulation where mutual interactions between navigation and flight control are critical in terms of stability. The tests underline the applicability of the presented approach, making this method ready for automatic camera-based flights