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Rebuilding Notre Dame, stone by virtual stone

The limestone vaults of the Notre Dame Cathedral, photographed before the devastating fire of April 2019. A global team of scholars and software engineers are working to restore the sanctuary.
The limestone vaults of the Notre Dame Cathedral, photographed before the devastating fire of April 2019. A global team of scholars and software engineers are working to restore the sanctuary.Andrew Tallon/Mapping Gothic France

The story of the Paris firefighters who dodged orange-blue “raindrops” of burning lead as they raced to save the Notre Dame Cathedral from ruin last year is well known.

Less heralded, though, is the tale of a second ring of guardians hoping to give the church new life.

Just hours after the flames were extinguished, a circle of scholars and software engineers around the world began work on an extraordinary, high-tech restoration effort that could lay the groundwork for rescuing other lost or damaged cultural treasures.

In France, Livio De Luca, research director at the National Center for Scientific Research, is leading the creation of a “virtual twin” of Notre Dame — an immersive virtual-reality replica that will help guide the resurrection of the sanctuary.

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The ever-changing simulation will be updated in real time with images from robot-borne cameras crisscrossing the burnt-out structure as the reconstruction progresses.

The virtual cathedral and its vast database feature “thousands of digital resources — photographs, point clouds, architectural surveys, and scientific analyses,” says De Luca.

Architects, archaeologists, sculptors, and restoration specialists across France, and later worldwide, will plug into the simulation — digitally rebuilding the cathedral, stone by stone, vault by vault.

As they map out the construction sequence, artisans organized by the French Ministry of Culture and specially trained in medieval stone carving techniques and intricate carpentry will repeat each step on the actual cathedral.

There is help coming from across the Atlantic, too.

Just after the fire, Andrew Anagnost, chief executive of the global software firm Autodesk, “called me and said this is a disaster,” recalls Nicolas Mangon, a French computer scientist at the company’s Boston Technology Center.

“We immediately offered our software for free to everyone involved in the cathedral’s restoration,” says Mangon, who heads Autodesk’s division for advanced 3-D modeling and virtual reality software for architects and engineers.

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Autodesk is overseeing the creation of a detailed, online model of Notre Dame that can be used to simulate the physics of the fire — on a laptop — and test the stability of the vaults and walls that were shaken during the inferno.

Mangon says the virtual Notre Dame could become a model for constructing digital replicas of ancient sites across the Middle East that have been buried by the sandstorms of time or by weapons of war.

Building this metaverse, he says, would make it possible to recreate the sites in the physical world at any point in the future.

And that could make the phoenix-like rebirth of Notre Dame a precursor for many more restorations.