Digitization of Notre-Dame Cathedral in Paris. Photo © Andrew Tallon
One of the most iconic symbols of Paris's architectural beauty and history, Notre-Dame Cathedral was destroyed by fire on Monday, April 15, 2019. The fire inside the 850-year-old Paris cathedral quickly spread throughout its largely wooden structure before it could be brought under control. A heritage monument that took almost 200 years to build was partially destroyed in just a few minutes.
While many objects inside Notre-Dame were saved by the 400 firefighters who tackled the blaze, the cathedral's spire, built in 1860, fell during the fire. Its roof also suffered extensive damage, including the wooden structure dating back to 1160, making it one of the oldest roofs of its kind in the world.
Although this is deeply saddening for all those who love this monument, there is a glimmer of hope in this dark cloud: France has already committed itself to rebuilding Notre Dame Cathedral. And, with today's construction technology, it's only a matter of time before Notre Dame is restored to its former glory.
More specifically, the combination of Building Information Modeling (BIM) and 3D laser scanning technology will make the reconstruction and restoration of the great cathedral relatively quick and easy.
Our Lady's saving grace
In 2015, architectural historian Andrew Tallon used a 3D laser scanner to map the entire cathedral, creating a precise image of the building that lives on in digital form. This detailed analysis, known as a point cloud, will serve as the basis for the entire reconstruction and restoration project, as it can show exactly what the building looked like - inside and out - so that all those working on its restoration can coordinate their efforts and work towards the same result.
Find out more: How can 3D laser scanning help restore old buildings?
What is 3D scanning?
3D scanning, as used in construction, is a three-stage process:
Scanner - Using a 3D laser scanner, millions of measurement points are quickly collected and saved. Once measured, these points resemble a "cloud" and provide an accurate 3D representation of the area scanned. To create a point cloud of a large, irregular space like Notre Dame, the scanner would have been placed in several different locations, creating overlapping point clouds that need to be combined.
Save - Once a series of point clouds has been downloaded from the 3D scanner, the scanning software can then "assemble" the individual stations into a single 3D point cloud model. This is known as "registration" of the scans. Once saved, the 3D point cloud can be exported to other applications as is, or detailed using modelling software to create intelligent modelled objects.
Detailing - Detailing a 3D point cloud involves using detailing software to transform the various components captured by the scanner into data-rich BIM components that can then be manipulated in a thousand ways to inform construction documentation, fabrication, assembly and installation, and much more.
How can 3D scanning save Notre Dame?
In 2015, Tallon completed the first and second stages of this process. This gives restoration contractors a head start, as they can simply detail the existing 3D point cloud to generate a fully functional buildable model that can be used throughout the rebuild.
3D scanning is commonly used throughout the construction process, whether for new builds, renovations or restoration projects. Prior to restoration, scanning a structure can help to record, maintain and preserve the appearance of existing building elements. Complete 3D site models created from these scans can aid in the design and construction process to help plan the details of a new structure. In the restoration and heritage fields, they can also record spatial and physical information about a building, or help conservators identify problems and find solutions.
Digital preservation is a related concept in the disciplines of heritage and archaeology. It uses 3D scanning in conjunction with digital film and photography to build up a complete representation of a site or structure. This enables archaeologists not only to see the site as it is today, but also to digitally reconstruct what it would have looked like hundreds or thousands of years ago.
While the damage to Notre-Dame Cathedral this week is regrettable, it's exciting to see that the effective use of modern construction technology can essentially turn back time for the famous monument. We look forward to seeing it restored to its former glory, thanks in part to BIM technology and 3D laser scanning.
