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Actor followed by drones
Walking the drones (Photo: Alonso-Mora)

Using a small fleet of drones, Dr. Javier Alonso-Mora presents a new system to track the motion and pose of an actor from the sky.

Special effects: almost no movie is produced without them. A virtual set is created in which actors, maybe in the form of some humanoid character, play their role. But how to reproduce the human motion in an alien flying a spaceship is everything but simple. Sensors are attached to the joints of the actor. Furthermore, Dr. Alonso-Mora explains that a fixed device, at a known location, then keeps track of the position of all of them. The main disadvantage of this technology, although extremely diffused, is that it cannot be used everywhere. Actors cannot move outside the studio, otherwise the signal would be lost.

A new study focusing on the use of drones to actively reconstruct the motion of a person through space has been recently published by Dr. Alonso-Mora, from the Faculty of Mechanical Engineering in collaboration with the Advanced Interactive Technologies (AIT) lab. In ETH Zurich.

Flycon demo

Making the system mobile
The idea to have a mobile system led Dr. Alonso-Mora and his team to mount the tracking devices on drones. At least two, to be precise. The way the system works is quite ingenious. Drones look at “markers”, Dr. Alonso-Mora says. These are beacons placed at specific locations, generally the joints of the actor. A single drone measures the distance between it and the marker, by measuring the intensity of the marker’s signal. But this is not enough to determine the position in three dimensions. A second drone must fly in formation with first one. This second aircraft also measuring the distance to the marker enables the system to obtain the position in 3D of the subject.

man with drones
Actor followed by drones (Photo: Alonso-Mora)

Interestingly, the drones have no idea where they are. Their entire world is the actor. Of course the drones know where the ground is, what their speed is and if there are any obstacles to avoid. However, precise GPS coordinates are unknown to the system. Dr. Alonso-Mora explains that it is, in fact, not needed. “For animation movies, the environment is all created artificially. So, what you need is the movement of the person and his joints, so that the character can move in the same way as the person.” But indeed, global localization is another problem in robotics. For a future iteration, the system could be coupled to a GPS receiver.

And how does the system make sure that the subject stay in the field of view of the drone? Dr. Alonso-Mora used the results of a previous paper of him and his team. They developed an algorithm to predict the position of the person one second in the future. The drone analyses the current position of the person and its movements and can estimate real time how the person will move. Then, the system takes action to keep the actor in view.

What's next?
The system consists mainly of commercial off-the-shelf drones which require minimal modifications. Thus, the cost of this system can be much lower than the state-of-the-art fixed cameras. Furthermore, applications of this technology are not only limited to film making. The analysis of the motion of athletes or animals are very interesting applications to consider. One of the colleagues of Dr. Alonso-Mora is opening a start-up, hoping to make this technology widely available. For now, it remains confined to its experimental status, but hopes are high that, very soon, these drones will be widely available on the market.

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