@article {2019g-WalStaFraSas, title = {UVDAR System for Visual Relative Localization with application to Leader-Follower Formations of Multirotor UAVs}, journal = {IEEE Robotics and Automation Letters}, volume = {4}, year = {2019}, month = {02/2019}, pages = {2637-2644}, abstract = {A novel onboard relative localization method, based on ultraviolet light, used for real-time control of a leader- follower formation of multirotor UAVs is presented in this paper. A new smart sensor, UVDAR, is employed in an innovative way, which does not require communication and is extremely reliable in real-world conditions. This innovative sensing system exploits UV spectrum and provides relative position and yaw measurements independently of environment conditions such as changing illumination and presence of undesirable light sources and their reflections. The proposed approach exploits this re- trieved information to steer the follower to a given 3D position and orientation relative to the leader, which may be considered as the main building block of any multi-UAV system operating with small mutual distances among team-members. The proposed solution was verified in demanding outdoor conditions, validating usage of UVDAR in real flight scenario and paving the way for further usage of UVDAR for practical multi-UAV formation deployments.}, doi = {10.1109/LRA.2019.2901683}, attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2019g-WalStaFraSas-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2019g-WalStaFraSas.mp4}, author = {Viktor Walter and Nicolas Staub and Antonio Franchi and Martin Saska} } @conference {2018k-WalSasFra, title = {Fast Mutual Relative Localization of UAVs using Ultraviolet LED markers}, booktitle = {2018 International Conference on Unmanned Aircraft Systems}, year = {2018}, month = {06/2018}, pages = {1217-1226}, address = {Dallas, TX}, abstract = {This paper proposes a new methodology for out- door mutual relative localization of UAVs equipped with active ultraviolet markers and a suitable camera with specialized bandpass filters. Mutual relative localization is a crucial tool for formation preservation, swarming and cooperative task completion in scenarios in which UAVs share working space in small relative distances. In most current systems of compact UAV swarms the localization of particular UAVs is based on the data obtained from motion capture systems for indoor experiments or on precise RTK-GNSS data outdoor. Such an external infrastructure is unavailable in most of real multi- UAV applications and often cannot be pre-installed. To account for such situations, as well as to make the system more autonomous, reliance on onboard sensors only is desirable. In the proposed approach, we rely on ultraviolet LED markers, that emit light in frequencies that are less common in nature than the visible light or infrared radiation, especially in high intensities. Additionally, common camera sensors are sensitive to ultraviolet light, making the addition of a filter the only necessary modification, keeping the platform low-cost, which is one of the key requirements on swarm systems. This also allows for a smaller size of the markers to be sufficient, without burdening the processing resources. Thus the proposed system aspires to be an enabling technology for deployment of large swarms of possibly micro-scale aerial vehicles in real world conditions and without any dependency on an external infrastructure.}, attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2018k-WalSasFra-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2018k-WalSasFra.mp4}, author = {Viktor Walter and Martin Saska and Antonio Franchi} } @conference {2018l-WalSasStaFra, title = {Mutual Localization of UAVs based on Blinking Ultraviolet Markers and 3D Time-Position Hough Transform}, booktitle = {14th IEEE International Conference on Automation Science and Engineering}, year = {2018}, month = {08/2018}, address = {Munich, Germany}, abstract = {A novel vision-based approach for indoor/outdoor mutual localization on Unmanned Aerial Vehicles (UAVs) with low computational requirements and without external infras- tructure is proposed in this paper. The proposed solution exploits the low natural emissions in the near-Ultra-Violet (UV) spectrum to avoid major drawbacks of the visible spec- trum.Such approach provides much better reliability while be- ing less computationally intensive. Working in near-UV requires active markers, which can be leveraged by enriching the infor- mation content through blinking patterns encoded marker-ID. In order to track the markers motion and identify their blinking frequency, we propose an innovative use of three dimensional Hough Transform, applied to stored position-time points. The proposed method was intensively tested onboard multi-UAV systems in real-world scenarios that are very challenging for visible-spectrum methods.The results of our methods in terms of robustness, reliability and precision, as well as the low requirement on the system deployment, predestine this method to be an enabling technology for using swarms of UAVs.}, attachments = {https://homepages.laas.fr/afranchi/robotics/sites/default/files/2018l-WalSasStaFra-preprint.pdf , https://homepages.laas.fr/afranchi/robotics/sites/default/files/2018l-WalSasStaFra.mp4}, author = {Viktor Walter and Nicolas Staub and Martin Saska and Antonio Franchi} }