  Autonomous exploration using unmanned aerial vehicles (UAVs) is essential for
various tasks such as building inspections, rescue operations, deliveries, and
warehousing. However, there are two main limitations to previous approaches:
they may not be able to provide a complete map of the environment and assume
that the map built during exploration is accurate enough for safe navigation,
which is usually not the case. To address these limitations, a novel
exploration method is proposed that combines frontier-based exploration with a
collector strategy that achieves global exploration and complete map creation.
In each iteration, the collector strategy stores and validates frontiers
detected during exploration and selects the next best frontier to navigate to.
The collector strategy ensures global exploration by balancing the exploitation
of a known map with the exploration of unknown areas. In addition, the online
path replanning ensures safe navigation through the map created during motion.
The performance of the proposed method is verified by exploring 3D simulation
environments in comparison with the state-of-the-art methods. Finally, the
proposed approach is validated in a real-world experiment.
