3.4.4. Hovering

This state handles the case when the vision data coming from the camera have not been updated for more than a second. In that case, the quadrotor is asked to keep its position for a certain period until the vision system is back online, sending again the required data. Then, once the feedback is restored, the quadrotor will resume its mission.

#### 3.4.5. Descending

This state gets triggered if the quadrotor is tracking the landing platform under a certain threshold and for a number of consecutive frames, but its current altitude is over the ideal horizontal maximum tracking altitude. The altitude waypoints are autonomously adjusted by being decreased by 0.1 m at each iteration.

#### 3.4.6. Ascending

This state gets triggered if the quadrotor has no visual contact with the landing platform for a number of consecutive frames, and its current altitude is below the ideal horizontal minimum tracking altitude. The altitude waypoints are autonomously adjusted by being increased by 0.1 m at each iteration.
