Riku Funada Maria Santos 0003 Takuma Gencho Junya Yamauchi Masayuki Fujita Magnus Egerstedt Visual Coverage Maintenance for Quadcopters Using Nonsmooth Barrier Functions. 3255-3261 2020 ICRA https://doi.org/10.1109/ICRA40945.2020.9196650 conf/icra/2020 db/conf/icra/icra2020.html#Funada0GYFE20