How 3D scanning techniques are helping to restore the Gothic masterpiece of Notre Dame

Posted by Derek Mason

9th November 2021

Photo credit: Photo by Sebastien on Unsplash

When flames ripped through Notre Dame cathedral in April 2019, it wasn’t clear that the structure would be saved. But although the spire and part of the roof were destroyed, with damage throughout, the fire was put out in time to save the landmark building and restoration is now underway.

In fact, with an intensive 5-year restoration mapped out, the plan is that the cathedral should be ready to receive visitors when Paris hosts the summer Olympics in 2024. That may be a little optimistic, but it will be interesting to see whether the project is delivered on time.

What is fascinating about the restoration, is that this historic structure – which was a real feat of engineering when it was originally built in the 12th and 13th centuries – is being restored using digital tools that its original master building team could only dream of.

At the heart of the work is Building Information Management (BIM). The restoration teams have access to a 3D ‘digital twin’ of the cathedral. In fact, thanks to the work of the late art and architectural historian, Andrew Tallon, there is an existing pre-fire laser scan of the building – taken in 2015 – as well as a post-fire scan taken via drone survey.

3D scanning techniques from both the ground and at drone level have gathered the millions of coordinates needed for the high-density spatial imaging. For Notre Dame, this modelling was done in Autodesk Revit software. However, the ornate spire that was destroyed, had to be modelled with Autodesk Maya.

After initially opening a global competition for new designs for the spire, the decision was made to rebuild an identical spire, and this will be constructed using wood timbers. To help keep the project on track, more than 1,000 French oak trees have already been felled. This means they can be dried for 18 months, so that tree sap and moisture doesn’t enter the wood fibres.

The BIM model helps with these kinds of logistics – making it easier to get clear on planning and sequencing in the construction work. Plans can also be made with safety and risk management in mind. It also helps to streamline workflows between all the different teams involved in the project. And, of course, the BIM model will play a critical role in planning a fire prevention system that is as close to perfect as possible.

Restoring a Gothic masterpiece is not easy, and there are more than 12,450 objects that were created for the BIM model. The team has also discovered that out of 180 cathedral vaults, not one is the same. Every single one is different in some small way.

The BIM model itself is almost 1GB of data – giving you some idea of how much data has gone into the Notre Dame’s digital twin.

This is technology we use ourselves, most recently in an extension project on a property overlooking Hyde Park in London. What is striking is the accuracy of the information. Vast numbers of coordinates are scanned very quickly, and you can view what you plan to build in a virtual world. The accuracy of the modelling is incredible.

The growth of BIM – and the use of it in a wide range of projects – shows us where technology is heading. These tools will increasingly shape the world of architecture, construction and engineering – as we create perfect digital replicas of existing buildings, and then explore and alter them in virtual reality.

There’s a long way to go before we’re all using these tools on every project. And there are problems to be ironed out – not least how you keep these models secure when multiple teams are using one model. But the technology is here to stay, and we all need to keep up to speed with it!

Meanwhile, if you need assistance with the structural elements of an upcoming project – with or without BIM modelling – please do get in touch.

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