From Stone to Pixels: Digitizing the Decor of Notre-Dame de Paris

Before the fire, the interior of the building was already blackened by dust and pollution, obscuring details of the sculpted elements located high above. Starting in 2021, scaffolding erected for restoration work allowed researchers to approach previously inaccessible decorative tops of columns and undertake their digitization.

“We used 3D photogrammetry to quickly create models. This technique involves capturing a multitude of images around objects. Software then analyzes these images, identifying common points to generate a 3D model. This model is subsequently textured and colored based on the initial photographs,” explains Grégory Chaumet, a PhD art history and Plemo 3D engineer.

To complement this approach, researchers employed another technique: lasergrammetry. Using a laser scanner that operates wirelessly, they had greater mobility for scanning complex objects, such as decorations ranging from a few centimeters to 1.5 meters in diameter. Over three years, Grégory Chaumet and postdoctoral researcher Denis Hayot scanned more than 300 decorative column tops, along with other sculptural elements. This work required the team to adapt to the logistical constraints of the restoration site while juggling the demands of other parallel research projects undertaken by Plemo 3D.

Digital surveys of the cathedral’s decor have revealed tool marks and assembly traces, providing invisible clues about the building’s construction. For example, researchers observed that in the monument’s choir, the oldest columns integrate the astragal—a molding at the base of decoration—into the same stone block as the column itself.
“This is a technique typical of ancient architecture,” says Dany Sandron.

This rare observation in medieval constructions challenges the notion of a break between Antiquity and the Middle Ages. “We thought the Middle Ages had severed ties with ancient knowledge, but these findings reveal a continuity of techniques and influences,” he adds. “This offers a more enlightened and nuanced view of the Middle Ages, often negatively portrayed. It’s essential to understand that historical periods don’t change abruptly, and there’s never a complete break, as is often assumed with major artistic movements,” the researcher explains.

Although access to the cathedral is now restricted for the final phase of reopening preparations, the team is determined to continue its research. “We’ll be able to resume work after the reopening, in a few months, during the restoration of the cathedral’s exterior,” assures Dany Sandron. This final restoration phase will focus on rebuilding the flying buttresses, which were already in poor condition before the fire.

Long-Term Multidisciplinary Research

To continue unraveling Notre-Dame’s secrets, the researchers collaborate with other teams, such as those from Sorbonne University’s Faculty of Science and Engineering and other French and international institutions, including the Historical Monuments Research Laboratory.

“There is genuine interdisciplinarity, with heritage professionals working alongside geologists, chemists, physicists, historians, and others,” says the researcher.

“We’ve also collaborated with Sorbonne University’s FabLab to create a 3D-printed segment of a capital from laser scanner surveys,” adds Grégory Chaumet.

A project to establish a permanent national thematic multidisciplinary network modeled on Notre-Dame’s scientific restoration initiative is currently under evaluation. This network would bring together complementary scientific and restoration expertise with specialized working groups on topics like decor and stained glass. “If we work on a cathedral like Reims or Amiens, which have even more imposing portals than Notre-Dame, it would be a shame not to leverage the expertise gained over the past five years,” emphasizes Dany Sandron.