Mapping on the Fly: Real-Time 3D Dense Reconstruction, Digital Surface Map and Incremental Orthomosaic Generation for Unmanned Aerial Vehicles.

The reduced operational cost and increased robustness of unmanned aerial vehicles has made them a ubiquitous tool in the commercial, industrial and scientific sector. Especially the ability to map and surveil a large area in a short amount of time makes them interesting for various applications. Generating a map in real-time is essential for first response teams in disaster scenarios such as, e.g. earthquakes, floods, or avalanches or may help other UAVs to localize without the need of Global Navigation Satellite Systems. For this application, we implemented a mapping framework that incrementally generates a dense georeferenced 3D point cloud, a digital surface model, and an orthomosaic and we support our design choices with respect to computational costs and its performance in diverse terrain. For accurate estimation of the camera poses, we employ a cost-efficient sensor setup consisting of a monocular visual-inertial camera rig as well as a Global Positioning System receiver, which we fuse using an incremental smoothing algorithm. We validate our mapping framework on a synthetic dataset embedded in a hardware-in-the-loop environment and in a real-world experiment using a fixed-wing UAV. Finally, we show that our framework outperforms existing orthomosaic generation methods by an order of magnitude in terms of timing, making real-time reconstruction and orthomosaic generation feasible onboard of unmanned aerial vehicles.