Inside the Model That May Help Restore Notre Dame

Ubisoft and Dassault modeled the cathedral, but one academic laser-scanned the entire iconic structure.

A point-cloud scan taken from Andrew Tallon’s scans of the Notre Dame Cathedral. (Image courtesy of Vassar University.)

A point-cloud scan taken from Andrew Tallon’s scans of the Notre Dame Cathedral. (Image courtesy of Vassar University.)

All eyes of the world watched in horror as Notre Dame Cathedral, as much an icon of Paris as is the Eiffel Tower, was engulfed in flame. The spire collapsed and the roof was destroyed. French President Emmanuel Macron announced the country would rebuild the cathedral “in five years.” After the announcement, attention has shifted to pre-existing digital models of the structure. Ubisoft Games’ model of the church has attracted a lot of new coverage, as has Dassault Systemes’ interactive representation of its construction. But perhaps one of the most detailed models of the church was created by one passionate academic, art professor Andrew Tallon.

Ubisoft Games has publicly pledged to donate €500K to the restoration, in honor of their Assassin’s Creed game set during the French Revolution. The game features a detailed digital rendering of the cathedral, one that game fans speculated might be used in the reconstruction. But the developers themselves have said that they’re not currently involved; the game’s rendering, while beautiful, simply isn’t detailed enough to help rebuild the structure.

A still image from Dassault’s Paris 3D interactive model of Paris through the centuries, showing the facade of Notre Dame. (Image courtesy of Dassault.)

Dassault Systemes, who offered their help and software to rebuild the church, has a long history with the church. Back in 2014, the company put out Paris 3D: an interactive 3D model of Paris throughout history, which shows the building of Notre Dame amidst other attractions in the city. 

To do that, the company’s team looked at old maps, city records, and archaeological drawings, and had a scientific panel to solve debates about the model. The digital reconstruction was made for accuracy, not entertainment, and it took twenty experts two years to assemble.

Dassault’s 3D Paris model, showing the building of Notre Dame in “4D”. (Video courtesy of Dassault.)

Company CEO Bernard Charles has offered the company’s 3DEXPERIENCE platform, its 3D robotic simulation modeling and its collaborative 3D project to the rebuilding effort, but did not specifically offer the “3D Paris” model.

But perhaps the most ambitious model of the structure is the one created by Andrew Tallon, a Professor of Art at Vassar University. In 2015, Tallon became the first person to laser-scan the cathedral, creating a digital replica with over a thousand data points.

Tallon created a point-cloud model of the church with a laser scanner, setting up the scanner at 50 different points within the church over the course of five days. The scanner would send out laser beams and measure the time it took to reflect back off of a solid surface, building a map out of the XYZ coordinates of surfaces. In a 2014 paper detailing his scanning process Tallon said that the margin of error on his scans was “often fewer than five millimeters,” and said that he used scanners from both Leica Geosystems and Faro to complete his scanning work.

Currently, much of Tallon’s data sits on hard drives at Vassar, not yet in usable form. While point clouds are a useful way of accurately mapping spaces, the clouds eventually need to be “connected” into a usable model with CAD software (Tallon’s writings indicated that he preferred AutoCAD). Point cloud maps are data-rich—Tallon’s map apparently contains a terabyte of data—and the conversion process could be lengthy.

Despite the effort it will take, Vassar is enthusiastic about the possibility of using Tallon’s scans to help restore the church. They believe it’s a fitting legacy for a man so passionate about understanding old buildings. “He was a very special human being who loved these buildings and wanted to understand them better,” said engineer colleague John Ochsendorf. “He wanted to be able to walk in the shoes and in the minds of the builders of the gothic. And he came as close to just about anyone to doing that.”