Fatshimetrie —
After a catastrophic fire five years ago, Paris’s Notre Dame Cathedral reopened this month, virtually unchanged from how it looked when it was built in 1163.
The massive reconstruction project was a testament not only to the hard work of the French people, but also to the lasers, drones and other advanced technologies that gave builders a window into the building’s past.
“The timeline would not have been possible without the records of what existed,” Amy Bunszel, executive vice president of architecture, engineering and construction at 3D software company Autodesk, told CNN. Her company played a major role in creating a model of the building as it existed before the fire, giving the reconstruction effort a kind of guide for what to do. “That would have required a lot more guesswork. Imagine using millions of tourist photos [as a reference point] instead of having a perfect, consolidated representation.”
Technology has helped France meet President Emmanuel Macron’s ambitious goal of rebuilding the monument in five years. It required teams from multiple companies combining damage assessments, specially created maps and advanced techniques now used in everything from film animation to construction.
A billion laser dots
The rebuilding, in some ways, began before the fire. Luckily, in 2015, art historian Andrew Tallon had painstakingly scanned the building with lasers. Tallon, a specialist in Gothic architecture, was interested in understanding how medieval builders erected some of Europe’s great cathedrals.
His initial effort, four years before flames engulfed the cathedral, required 12 lasers and a team of seven engineers to scan the building and collect 46,000 images, Bunszel said. The spatial map he created used more than a billion laser-measured points, and it revealed some previously unknown details of the cathedral, such as the fact that the interior columns on the cathedral’s west end are not aligned.
Tallon died in 2018, just months before the April 2019 fire that shocked Paris. By the time hundreds of firefighters had brought the flames under control, most of the structure had been destroyed, including the famous 315-foot spire that had collapsed through the roof.
While its detailed scans revealed a lot about the ancient structure—which has undergone countless modifications and small changes over the centuries—they weren’t enough on their own to build the kind of detailed model that would be needed to restore Notre-Dame.
That’s where Autodesk came in. After the fire, Autodesk worked with French laser company AGP to set up scanners around the cathedral and capture billions of points needed to create a full-scale digital model. The companies donated their services to Rebâtir Notre-Dame, the public institution that led the restoration efforts.
The post-fire process wasn’t always easy, Bunszel said.
“The cathedral was very unstable right after the fire,” Bunszel said. “They had to build temporary structures and scan continuously during the rebuilding process.”
Piecing together the story
Eventually, the full view was captured by superimposing new laser scans and drone images on top of Tallon’s earlier scans.
Because of Notre-Dame’s complexity, structural detail, and size, it took the companies more than a year to create the new 3D model. Compared to traditional methods of documenting historic structures, these types of scans speed up the process considerably. Notre-Dame also required continuous sweeping.
While the new cathedral looks nearly identical to the original, a few areas have been modernized: the addition of sprinkler and fire suppression systems, optimized lighting placement, and a cleaner appearance thanks to years of less soot from candles and operation.
The plaza in front of the cathedral was also redesigned with the help of Autodesk technology. The company supported four competing teams to create 3D visualizations of their proposals before receiving public feedback, and a winner was ultimately chosen.
Looking at this stunning reconstruction of Notre-Dame Cathedral in Paris after the 2019 fire, it’s clear that the use of advanced technologies like lasers and drones played a crucial role in preserving the historic heritage for future generations. The combination of human expertise and technological innovation has made it possible to accurately capture the smallest details of this architectural gem, offering an exciting new perspective on how the past can be restored for the future.