**4.2 Six rotors tracking**

This experiment has the particularity of that the UAV to avoid detection flies hidden behind the trees, after which it starts a free flight. And in both cases the particle estimator is able to detect when only one part of its image visible. From the moment of the first detection the particle estimator remains locked throughout the entire flight. The **Figure 8** shows part of the frames sequence of the flight, from left to right and from top to bottom the "UAV" first flying behind the trees, while the particle estimator begins distributing the particles in the largest possible area of the screen, after the third frame, and with the "UAV" still largely behind the trees, the particle estimator still able to detect it and "hook" it as soon as it partially appears.

From the fourth frame the estimator remains locked during the whole flight, especially when the occlusion free flight is carried out, and the tracking is always right.
