  In this article, we propose a control solution for the safe transfer of a
quadrotor UAV between two surface robots positioning itself only using the
visual features on the surface robots, which enforces safety constraints for
precise landing and visual locking, in the presence of modeling uncertainties
and external disturbances. The controller handles the ascending and descending
phases of the navigation using a visual locking control barrier function (VCBF)
and a parametrizable switching descending CBF (DCBF) respectively, eliminating
the need for an external planner. The control scheme has a backstepping
approach for the position controller with the CBF filter acting on the position
kinematics to produce a filtered virtual velocity control input, which is
tracked by an adaptive controller to overcome modeling uncertainties and
external disturbances. The experimental validation is carried out with a UAV
that navigates from the base to the target using an RGB camera.
