At the Cité de l’architecture, the scientific secrets of Notre-Dame de Paris revealed in virtual reality

When they enter the room, called the “Téléport l’Exaltemps”, within the City of Architecture and Heritage, visitor-explorers can hardly imagine with what ease, within a small room , they will be able to travel in space and time. For forty-five minutes, equipped with a backpack and a virtual reality headset, they can wander through the central corridor of the Notre-Dame de Paris cathedral, looking at the smallest details right down to the faces of the onlookers present. … in 2012!

This virtual teleportation is possible thanks to the work of Andrew Tallon, an American professor passionate about Gothic art. Between 2006 and 2012, he produced the most accomplished 3D capture of Notre-Dame de Paris by placing his measuring instruments using lasergrammetry in around fifty different locations, inside and outside the cathedral. . More than a billion points were collected and synthesized into a “cloud”. Having died in 2018, a year before the fire, could the historian imagine to what extent his digitization work would be essential for scientists?

Science at the service of the restoration of Notre-Dame de Paris

Based on the laser survey carried out by Andrew Tallon, various laser and drone photogrammetry campaigns were carried out by the CNRS on the remains, after the 2019 fire, and throughout the reconstruction. To the nearest millimeter, these billions of points were compiled to create a virtual twin, on a 1I1 scale (real size), which constitutes the heart of the exhibition.

But more than the contemplation of a digital double, it is the foray into scientific data that is fascinating in this exhibition. Indeed, for several months, the Dassault System teams and the CNRS “digital data” working group conducted workshops at the Exaltemps Teleport with different teams (architecture, materials, structure, archaeology, etc.) mobilized within the scientific and restoration project of Notre-Dame de Paris.

These workshops made it possible to bring scientists together by facilitating and enriching their interdisciplinary exchanges, thanks to simulation and collective virtual reality tools. Concretely, this involves, for example, analyzing the construction of the old framework using samples taken from the calcined beams; virtually manipulate remains of charred beams in order to find their original location; simulate the actions of water and fire on the structure of the cathedral…

The virtual reality experience therefore offers the general public a unique point of view on this scientific research and this documentation work underway on the site. A visit which is destined to evolve, since the idea is to continue to follow the scientific work as well as the digitization and documentation of the key stages of the restoration.

A fun dive into a complex subject

From the start, the wish was to stand out from the entertaining immersive experience Eternal Notre-Dame in order to highlight the work of scientists. While there was a risk of confusing visitors with complex data, the exhibition succeeded in popularizing and making accessible this research work carried out over the last five years during the restoration project.

Accompanied by a guide-lecturer, 3D visualization makes it possible to bring to life these elements which are therefore not only of interest to scientists. The explanations on the concept of Lidar (laser remote sensing), the interest of point clouds, the objectives of collaborative work as well as the various experiments carried out appear clear and clear. Everything is done to better understand their tools in a fun way: the visitor changes scale and altitude, watches a visual restitution of the dating of the elements of the framework, travels in time as the construction site progresses , or even handles charred elements. A technical challenge which partly explains the high price of the experience (€32).

The preview view of the restoration of a chapel is moving: it makes concrete the work carried out to recover the vibrant colors of the old paintings. A great way to wait before the reopening of Notre-Dame de Paris, scheduled for December 8, and to see these splendid restorations “in real life”.