In 2010, Vassar College Professor of Art History Andrew Tallon used a 3D laser scanning device to digitally map every square inch of Paris’ Notre Dame Cathedral.
An art historian with a focus on French Gothic architecture, Tallon hoped the laser scan would help him decipher subtle changes to the structure as it aged. What he didn’t know at the time (or before his passing in 2018) was just how pivotal his scan — and the technology behind it — would become.
April 15, 2020 marks the one-year anniversary of the fire that damaged Notre Dame’s iconic roof and spire. And as officials look to rebuild the 850-year-old structure1, Tallon’s work could serve as a valuable resource to help give the Cathedral new life. But there are still many tasks to complete before any rebuilding begins. For example, removing some 40,000 pieces2 of damaged scaffolding—amounting to 250 tons—to avoid further damage. However those efforts, scheduled to begin on March 233, have been delayed indefinitely due to safety concerns amid the COVID-19 crisis.
Tallon did not initially intend for his digital copy of Notre Dame to be used for restoration. Instead, he created the digital scan to inform the images included in his 2013 book (co-authored), Notre Dame de Paris4. Lindsay Cook, recently published a translation5 of the book earlier this year. Cook is a visiting professor of Art History at Vassar who worked closely with Tallon to digitally map Notre Dame Cathedral.
“It was his interest in flying buttresses and gothic structures in general that led him to make this scan,” says Cook. “So he was hoping, in taking stock of the building in that way and in such an accurate detail, that he would be able to understand small changes in construction over time. And he was able to see this in some of his scans.”
However, it’s exactly that detail of the scan that makes them a potential candidate for the restoration efforts of Notre Dame. While the exact size of the Notre Dame file is unknown, some of Tallon’s other work scanning cathedrals resulted in files over 100GB in size6. Moreover, in leveraging 3D laser-scan technology to create a digital copy of Notre Dame, Tallon combined the seemingly opposing disciplines of art and technology to pioneer a method for the future of historic preservation.
Measuring History with Precision
The scanning process itself was no easy feat—it required weeks of preparation and patience for Tallon to figure out how to best capture the Cathedral. Once he and his team were ready to begin, he mounted the scanner above his tripod and, over the span of five days, repositioned it in 50 different locations to build a digital reproduction of the Cathedral.
The laser scanner is the most advanced technology that exists to digitally capture intricately detailed structures, Tallon said in a 2015 video feature7. Capturing over one billion different data points, the device allowed Tallon to make specific conclusions about the structure with relative certainty. For example, the scans revealed that many of Notre Dame’s columns and aisles did not line up — masons appeared to have built the Cathedral around the remains of structures that had existed long before Notre Dame8.
Before laser scan technology, historians used advanced cameras to capture 360 degree photos. While these images appeared to present an accurate depiction of the Cathedral, they lacked 100% precision. Today’s laser scans can capture an accurate position for every pixel, up to the millimeter. That means even minute details, like the slightest curvature in the structure or discoloration of a material can be captured through laser scans.
This level of accuracy requires storage space—and processing power—to run efficiently. Thanks to today’s efficient storage capabilities, external hard drives have the processing power needed for the type of complex data Tallon’s laser scans produced.
“[Tallon] was always sort of, how should I put this — a hardware junkie,” Cook said. “He always wanted to get his hands on the latest new thing, even if it was going to be for a short period of time, or only to work on one building.”
Cook believes Tallon’s scans will become a valuable resource once France is able to begin restoring the parts of Notre Dame that were destroyed in the fire—but not for the purpose of restoring the original Cathedral’s construction, as some initially thought. Instead, the scans will be most useful for comparison: to track changes, particularly structural, that might have occurred over the years.
“There are other documents, of course, that speak to the way Notre Dame looked before the fire,” Cook says. “Drawings, plans, photographs, and all of those things serve the same purpose as a laser scan when it comes to viewing the building itself. But what the laser scan has going for it that those other documents don’t have is the ability to take a total sweep and compare the building overall before and after the fire.”
By telling a larger narrative about how the structure has changed over time, the technology can offer a glimpse into Notre Dame’s complex past, while informing its future.
“[Tallon] was fond of saying, ‘You can look back in time through a laser scan,’” said Michael T. Davis, Chair of Architectural Studies at Mount Holyoke College and one of Tallon’s colleagues. “You can see if the building has been deformed or where there are areas that might present structural distress. So, right around the center of the building, for instance, these laser scans can perhaps reveal what was happening in the structure of the building. And in going forward in a repair or reconstruction, one can take measures to correct or address those areas of structural weakness.”
Preserving the Past, Restoring the Future
Tallon was interested in capturing Notre Dame with his scanner because it presented an opportunity to unify the new with the old. “What he was essentially doing was using this cutting-edge technology that had a lot to do with the industry of our modern day, and applying it to historical artifacts,” Cook said.
And according to Davis, who accompanied Tallon on some of his digital scans of other gothic structures in France, this technology is just the beginning of a larger trend in historic preservation.
Several architectural historians are experimenting with technologies like LiDAR and Computer Aided Design (CAD) software to accurately capture the specific structural characteristics of a building, and record changes over a given period of time. As the Notre Dame fire illustrated, destruction can happen at any moment, and the ability to refer back to a digital copy of these structures is a valuable asset for historians.
But according to Cook, there’s also an ethical component to recreating lost structures through digital modeling. Because buildings change overtime, architects in charge of restoration efforts must determine whether to go back to mimic a specific moment in history, or to replace the lost pieces of a building with a more contemporary design.
“When we talk about restoration, it’s important that we determine what moment in time we’re trying to go back to,” Cook says. “What kinds of people and communities are we impacting when we make those decisions?”
As for this particular moment in time? Cook says the use of 3D scans to rebuild Notre Dame Cathedral will have monumental significance.
“If we look back in history there are certain decisive moments for the Cathedral,” she says. “And going forward I think we’ll look back on this moment — and this particular laser scan — as one of those decisive moments in the history of the Cathedral.”
This content is produced by WIRED Brand Lab in collaboration with Western Digital Corporation.
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