The indispensable role of point cloud data in rebuilding Notre Dame

Over five years after the devastating fire, the world-famous Notre Dame cathedral in Paris has reopened its doors. A cloud of one billion points was fundamental to enabling a full-blown digital recreation of the historical landmark’s interior and exterior. The data proved indispensable in the restoration project, which based on the first glimpse of the interior has been a resounding success.

On 15 April 2019, the Notre Dame went up in flames. The world watched in horror as the cathedral blazed for hours. A significant part of the cathedral was lost in the fire; the spire collapsed and the roof was destroyed. The subsequent years have been spent on the mammoth task of rebuilding Notre Dame. The spire has been rebuilt and the stained glass and woodwork have been restored. The work was financed entirely by donations from around the world. The total cost: around €700 million.

Terrestrial laser scanning

Following such disasters, terrestrial laser scanning (TLS) surveys allow accurate assessment of the damage, structural stability and required restoration work, but they cannot provide information about the pre-disaster state. However, in a stroke of luck in the case of Notre Dame, Prof Andrew Tallon – an architectural historian from Vassar College in the USA – had captured the entire cathedral using a terrestrial laser scanner in 2010.

His project was aimed at fully understanding the nature of the Gothic structure and identifying any structural anomalies. Laser scanning enabled Tallon to create a precise 3D model of Notre Dame, translating point clouds into detailed representations of its buttresses, ribbed vaults, stained glass, ornate carvings and other architectural details.

That accurate and detailed point cloud turned out to be of tremendous help in faithfully reconstructing Notre Dame in its original state. In fact, Tallon’s laser scans were the only really accurate as-built measurements of the cathedral.

The value of point cloud data

While modern restoration efforts can’t fully replicate the artistry of centuries past, Tallon’s scans provided an invaluable guide for the craftspeople involved, allowing them to come remarkably close. Although Tallon unfortunately passed away in 2018, his groundbreaking work remained a vital resource for restoring the iconic cathedral.

The answer to the question that arose after the devastating fire – “How could this historic cathedral, which had weathered centuries of challenges, ever reclaim its former glory?” – didn’t lie in ancient blueprints, but in the use of innovative digital technology: terrestrial laser scanning. This illustrates the urgent need for accurate and detailed 3D models of cultural heritage sites, before disaster strikes or the natural elements erode their splendour.