Time seemed to stand still for hours Monday as the Notre Dame Cathedral, a fixture of Paris’ skyline for centuries, went up in flames. Even though firefighters eventually got the fire under control and saved the religious relics inside, they could not save the cathedral's central spire.
All that remained on Tuesday was a charred husk of the iconic landmark.
While it’s anticipated that rebuilding could take years, there’s reason to be optimistic. That’s in part because over $700 million in funding has been pledged to the effort, but also because of the work of a historian who had the foresight to map every inch of the cathedral using a series of laser beams.
Using a laser, historian Andrew Tallon collected more than one billion data points by taking scans of various locations throughout the cathedral in 2015, according to this National Geographic profile. Then he wove all of them together to recreate the entire structure in striking, three-dimensional detail.
“I had to set up a network of targets, which are just geo-located points in space. And you define the density of the scan, the resolution of the scan – in other words, how many x, y, z coordinate points in the space you want to acquire – and then you let it rip,” he told National Geographic at the time.
Here’s how it works: the laser scan shoots out a beam and then records exactly how long it takes for the beam to hit its target and bounce back, Tallon said. He said it does the same thing over and over again, often “hundreds of thousands of times a second,” to generate a complete web of data points.
Once that part is done, all of those data points are assembled into a composite image. The end result is a flawless, life-like depiction of the 850-year-old cathedral.
That’s a good thing, too, because Tallon’s research uncovered loads of previously unknown information about the construction of Notre Dame. Even though he died in November, Tallon’s work combined with the fundraising campaign means the cathedral’s interior, roof and spire can all be restored in time.