Astrum: Turning Riyadh’s Skyline into a Living Planetarium

Light-artist László Zsolt Bordos has never shied away from big canvases—mapping entire cathedrals and skyscrapers is his specialty, but with “Astrum” he set his sights on the sky itself. Perched on Riyadh’s Al Faisaliah Tower, the piece uses 64 pan-tilt beams to track the Moon, planets and a few hundred stars in real time, essentially turning the skyline into a living planetarium and inviting viewers to reconnect with the timeless rhythm of the cosmos and their place within it. 

Getting that to work meant wrestling with celestial math, fixture limits, weather, and latency—a lot of heavy lifting TouchDesigner programmer András László Nagy tackled head-on. His TouchDesigner engine takes NASA ephemeris data, crunches it in real time, and feeds pan-tilt values to every fixture while still leaving room for on the fly adjustments. What emerges is a precision instrument doubled as a contemplative artwork: a planetary light compass that lets the Riyadh night skyline trace the slow dance of the cosmos.

"My role was to define the conceptual framework, to imagine a light sculpture that functions as a planetary compass. Astrum uses beams of light to point in real time toward specific celestial bodies, translating astronomical movement into a perceptible experience. The idea was to create a simple but powerful gesture: inviting people to look up and reconnect with the cosmos. The collaboration with András László Nagy allowed this vision to become mathematically precise and technically possible, translating astronomical data into a living, real-time system, while Balázs Varga established the lighting control framework, safeguarding and maintaining the system." - László Zsolt Bordos

 

https://vimeo.com/1168237607?fl=pl&fe=sh

 

 

TECHNICAL INNOVATION overview 

The system computes the position of 757 celestial bodies, each with its own trajectory, velocity, and orbital pattern. Relying on intense research, András determined the exact positions and trajectories of the celestial bodies, based on data collected from NASA's Deep Star Maps and other databases of the observable universe. The system continuously calculates the precise orientation of each beam, generating control data at every moment. This real-time celestial data stream is then integrated into a GrandMA lighting control pipeline, where lighting programmer Balázs Varga translates data into fluid, coordinated movement across all 64 beam fixtures.

The movement of the beam lights is not imposed artificially but emerges naturally from the rotation of the Earth and the orbital mechanics of the solar system. In this sense, the artwork is "performed" by the Cosmos itself.

Derivative: Can you explain a bit the impetus for this project and how it came about?

László Zsolt Bordos:  ASTRUM is a carefully designed concept meant to bring cosmic awareness into everyday (and every night) life, inviting viewers to contemplate the movement of the heavens and their connection to the Universe. 

Derivative: From a viewer’s perspective on the street, how evident is it that the beams are following actual celestial bodies rather than forming a random light sculpture? What design choices (beam width, labeling, real-time visualization, timing) help communicate that relationship?

András László Nagy: For most pedestrians in a city like Riyadh, I think only the Moon is clearly visible, and maybe some of the brighter planets can be seen through the air and light pollution. To help people understand more of the concept behind Astrum, we created a live stream directly from TouchDesigner, which visualized in real time the chosen celestial bodies and constellations.

Derivative: How did you play test this and what were the results from the testees/public?

András László Nagy: For a month, I was checking a few sky-view applications to see whether everything was running in sync with TouchDesigner. I only used the world clock data to rotate all the celestial bodies around the Earth based on their sidereal time.

Derivative: András, could you walk us through the technical workflow that lets each beam stay locked onto its assigned planet or star? What tracking data, motors, or feedback systems are involved?

András László Nagy: I used the 2020 star map from NASA to create a 3D star model in TouchDesigner. First, I tried to make a Heliocentric model. I had to understand the solar system from scratch. I made many attempts (and many errors) with a super-complicated rotational model. The fixtures were rotating with the Earth itself while trying to look at the rotating celestial object. It became so complex to calculate pan/tilt values like that, and I slowly realized that I had overcomplicated the system. So I changed my approach and started to build a model based on the relative movement of the sky as seen from a specific location on Earth, which we call a geocentric model. This was much easier, because in this model the fixtures are not moving at all, and everything else is moving around them.

To check if everything was correct, I built a previsualization in TouchDesigner with physical bodies of the lamps that were receiving pan and tilt values.

Derivative: At what point in the pipeline is TouchDesigner involved, and how does it manage live astronomical data, fixture control (DMX/Art-Net), and any visual previews or diagnostics the team relies on?

András László Nagy: TouchDesigner was clearly the nerve center of the installation. I sent dimmer and pan/tilt values to a grandMA, where Balázs Varga implemented some safety features. The lights we used, the Ayrton MAMBA lights were so powerful that the festival also had to ask permission from the airport to run the installation. It felt very strange to know that planes were flying at a higher altitude just to avoid beams that we were controlling from a tiny little computer.

We used sACN to communicate with the grandMA. TouchDesigner’s previsualization made it possible to apply show logic, e.g. dimming a beam if its target drops below the horizon or if the selected target is in a risky area.

The most challenging part of the patch was defining which planet or constellation should be selected for each group of lights. In the end, I created a rotating geometry with all the groups that could be selected for a specific fixture group.

Derivative: Can you walk us through the mapping from 3D celestial coordinates to pan/tilt DMX values: which CHOP chain handles that conversion?

András László Nagy: What I did was the following:

I searched for an HDRI space map containing detailed constellation data. Over several weeks, I manually placed each star in TouchDesigner, assigning precise positions and custom names.

To speed up the process, I developed a fast mapping system using a Hold CHOP to capture mouse values and a Replicator to replicate positions while mapping stars from the HDRI. Each accurately mapped star geometry was grouped and labeled according to its constellation.

After mapping all the stars, I converted the geometry into SOPs containing 97 points and primitive groups. This was a crucial step, as it allowed me to define which celestial body or constellation should be selected for each side of the building.

Next, I used a Sort SOP set to "Proximity to Point" to determine the order of celestial bodies closest to the sweet spot of the fixtures and the building. I then generated a DAT table containing all this information and created a selection path for each fixture that defined its look-at target.

Since the order of celestial bodies changes over time due to Earth's rotation, this data was continuously updated and distributed across all 64 fixtures.

For the pan/tilt calculations, I subtracted the XYZ position of each fixture from the selected celestial body to compute direction vectors.

• For PAN, I used a Function CHOP with atan2(tz, tx).

• For TILT, I first calculated the horizontal vector length using a Math CHOP combine length(tx, tz), then applied another Function CHOP with atan2(ty, length).

Finally, I remapped the resulting values to the fixtures’ pan/tilt ranges using Math CHOPs. To ensure safe operation, I implemented protective logic using Logic, Lag, Slope, and additional Math CHOPs. These safety systems automatically blackout the lights during excessively fast movements (to prevent unintended rotation paths) and define exclusion zones to protect pedestrians and the building.

Derivative: With 64 fixtures, how many universes are you streaming, and how did you structure the sACN out DAT(s) for reliability?

András László Nagy: The system used a total of eight DMX universes for the 64 fixtures. The output was generated in TouchDesigner using DMX CHOPs configured for sACN transmission.

Each universe was separated into its own DMX stream to keep channel ranges clearly structured.

Derivative: What guardrails did Balázs add in grandMA, and which of those could just as easily have stayed inside TouchDesigner?

András László Nagy: For safety reasons, it was important for us to have a proper lighting console in the system. We first monitored the outgoing DMX values from TouchDesigner in grandMA, and only after verifying that everything behaved correctly did we send the signal to the fixtures.

TouchDesigner was running continuously for two weeks, while grandMA effectively acted as a firewall and control layer. This allowed the technical team to start the show, test faulty fixtures, or shut down the system safely when necessary.

In theory, TouchDesigner could have handled everything on its own, but having dedicated hardware and software at the end of the signal chain made the system significantly safer and more reliable. In this setup, grandMA provided the stability and operational control required for a large-scale installation.

During the project, I often found myself wishing for something like a “TDeck” — a dedicated control surface for TouchDesigner with physical faders and buttons similar to a grandMA console, available globally for visual and lighting control in projects like this.

Derivative: Can you describe the TouchDesigner network that simulates the tower + beams? 

András László Nagy:The TouchDesigner network simulated both the tower geometry and the fixture beams in a simplified previs setup. Using the calculated pan and tilt values, I placed virtual fixtures inside TouchDesigner and applied these values directly to drive the geometry rotation, matching the real-world fixture behavior.

The fixtures were parented to the tower model, allowing the simulation to reflect the real installation layout and spatial relationships. Beam directions were generated from the same control data that drove the physical fixtures, ensuring that the virtual and real systems behaved consistently.

This setup allowed me to verify that all calculations were correct and that the fixtures would behave as expected before deploying the system on site, significantly reducing calibration time during installation.

Derivative: How did you align the virtual beam angles with real-world calibration—total-station survey, camera tracking, or manual tweak?

András László Nagy: I didn’t use total-station surveying or camera tracking for calibration.The system was driven purely by astronomical calculations based on the local time of the PC.

Using the computer’s local time as a reference, I calculated the real-time trajectories and angular velocities of the celestial bodies. Since both the virtual simulation and the physical fixtures were driven by the same mathematical model, the alignment between the virtual beams and real-world output was inherently consistent.

This approach eliminated the need for manual tweaking, as the accuracy came from the underlying coordinate and time-based calculations rather than external tracking or surveying systems.

Derivative: How do you deal with the atmosphere, light pollution, tower movement so the beams stay exactly on their targets all night?

András László Nagy: The atmosphere is tricky. When there is a lot of dust in the air, the beams are more visible, but they cannot reach so far, and the viewing distance becomes shorter. When the sky is clear, the beams are visible from farther away but appear less bright. We tried to measure how far 32 beams could travel and estimated approximately 10 km.

Once we were working on the run, in a minivan, traveling around the tower while making adjustments. It really felt like we were some kind of starlight hunters. :)

Derivative: What is the accompanying interface or app, signage etc that explaings to spectators which planet each beam is tracking and why that moment may be significant in the sky?

xAndrás László Nagy: The accompanying interface was also created in TouchDesigner and helped visitors understand which light beam corresponded to which celestial body. The interface provided contextual information in a simple and accessible way, allowing spectators to connect the moving beams with the actual objects in the sky.

Rather than emphasizing specific astronomical events or moments, the installation treats every moment as equally significant. Its intention was to remind people that, even through a light- and air-polluted urban sky, the stars are still present above us, and that we are continuously moving together through this vast space.

Derivative: Looking back, which part of the network are you proudest of, and which would you redesign if you had another month?

András László Nagy: Looking back, I’m most proud of the safety system built around the fixtures, as well as the star selection system that automatically determines the optimal “sweet spot” targets. Both parts proved to be very robust during long-term operation and were critical for making the installation reliable in a public environment.

If I had another month to refine the project, I would redesign the system to use POPs instead of converting everything to SOPs. At the time, I felt more confident working with SOP-based workflows, but in hindsight, a POP-based approach would have been more efficient and flexible for handling dynamic relationships and ordering between the celestial bodies.

Credits

Concept: László Zsolt Bordos

TouchDesigner Programming: András László Nagy

Lighting Operator: Balázs Varga

Technical Support: Media Pro

Principal Lighting Designer: Koert Vermeulen

Artworks Technical Director: Pedro Clavier

Liason: Garine Aivazian

Production: Kitija Vasiljeva

Curatorial Director: Lucrezia Cipitelli

Supervisor: Davide Carbone

Organized by: NOOR Festival 2025 Riyadh

Follow László Zsolt Bordos Website | Instagram | Vimeo

Follow András László Nagy Instagram