How Do a Thousand Drones Draw Pictures Without Colliding?

Hundreds of drones rising into the night sky to form letters and pictures is now a fixture of opening ceremonies and festivals. The question every time is the same. How do they not hit each other?

Intuitively it feels like the drones must sense one another and swerve. The reality is the opposite.

They don’t dodge — the paths are written so they never overlap

The core of a drone light show finishes inside a computer, not at the venue.

1. Turn the picture into coordinates. The shape you want (a logo, letters, a 3D model) is converted into a point cloud. One drone is one point. In a 500-drone show, every scene has to be expressible as 500 points
2. Match points to drones. There are countless ways to connect 500 points in scene A to 500 points in scene B. An assignment is computed so the total travel distance is minimised. Solving this well is what makes transitions fast and saves battery
3. Generate paths. A curve is drawn for each drone from A to B
4. Check for collisions. For every pair of drones, distances are computed over time to see whether any interval drops below the minimum safe separation. If one does, the path is revised and checked again
5. Upload the verified paths to each aircraft

In other words, no new decisions are made during the show. Each drone carries a table saying “at this second, I am here” and follows it. The reason is clear. Make hundreds of aircraft sense each other and decide on avoidance in real time and neither the computation nor the radio traffic is manageable — and one misjudgement cascades into a chain collision.

How is the positioning that accurate?

Ordinary GPS is accurate to a few metres. In a formation with two to three metres between drones, a few metres of error is a collision.

So they use RTK (real-time kinematic positioning). The principle goes like this.

• A ground reference station whose exact position is known is set up at the venue
• The reference station receives the same satellite signals. Because it knows its true position, it can compute how much error is riding on the received signal
• That error correction is broadcast to the drones in real time
• Each drone subtracts that error from its own GPS reading

Because receivers in the same area experience error sources such as atmospheric delay almost identically, this brings the error down to centimetres. Most of the reason a drone formation can hold a grid is here.

Colour and brightness

An RGB LED sits on the underside of each drone. Every drone carries not only coordinates but colour values over time. So the picture in the night sky is effectively an ultra-low-resolution display floating in the air. One drone = one pixel.

Constraints follow from that.

• The number of drones is the resolution. Writing legible letters takes numbers. With 100 you are limited to simple shapes
• Black cannot be rendered. The background is the night sky, so dark areas are handled by switching drones off or not placing them there
• Depth comes from brightness. To express a 3D shape, drones in front are made brighter and those behind dimmer

How failure is planned for

Hundreds of aircraft are in the air with an audience beneath them. Without safety design the show does not exist.

• Geofence: the flyable volume is defined in three dimensions, and any aircraft trying to leave it has its control cut automatically
• Per-aircraft fault detection: each drone monitors its own battery voltage, GPS reception and attitude error. Outside limits, it drops out of the formation and moves to a designated recovery point or descends
• Global abort: a command to land everything immediately is always ready at the ground station
• Spares: more aircraft are prepared than strictly needed so the picture does not collapse when one drops out

So when you see a few drones quietly disappear mid-show or a hole open in the picture, it is usually not an accident but a designed dropout.

What actually trips up operations

Site conditions cause problems more often than technology does.

Shows are short because of battery, not because of an artistic decision. For longer events, formations are split and flown in shifts, or the programme is built around short, strong scenes.

Will they replace fireworks?

Partly, already. With no pyrotechnics there is no smoke or noise, no debris is left, and they are possible in areas at risk of wildfire. The same equipment is reused, so unit cost falls as the number of performances rises.

What they cannot replace is equally clear. The physical concussion of a firework, its instantaneous brightness and the impact you feel in your body cannot be imitated by LEDs. So large events now mix the two: drones handle shape and narrative, fireworks handle the punch of the climax.

In short

1. Drones do not avoid each other. Collision-free paths are computed and loaded in advance
2. Centimetre precision comes from a ground reference station’s error correction (RTK)
3. One drone is one pixel. The number of drones is the resolution
4. A drone dropping out is usually a designed safety behaviour, not an accident
5. What decides show length and cancellation is not technology but battery and wind

Frequently asked questions

How many drones does it take to write letters?

A short word or a few letters is possible at 100–200 aircraft, but writing characters with many strokes, or several words legibly at once, takes hundreds. The further away the audience, the more aircraft are needed.

What happens if one falls?

Each aircraft is designed to detect a fault, drop out of the formation on its own and move to a designated point or descend. Keeping a safety distance between the audience area and the flight volume is a basic condition, and that distance is also managed as a permit condition.

Can an individual commission a small show?

Yes, through a specialist operator. But night flight authorisation, airspace coordination and securing a safety zone mean the lead time is not short, and there is often a minimum number of aircraft and a minimum fee. In a city centre or near an airport, approval itself may be difficult.

Why is rain an automatic cancellation?

Most light-show aircraft are not fully waterproof, and moisture is a direct cause of motor and board failure. On top of that, rain clouds usually bring wind, which makes holding formation difficult. Under safety rules, wind speed and precipitation are not negotiable — they are operated as cancellation thresholds.