Notre Dame to Syria: 3D reconstruction for restoration
— Research by Soumik Chakraborty
Through centuries of existence, Notre Dame has been the birthing place of history — Napoleon I was made emperor there in 1804 and Pope Pius X beatified Joan of Arc there in 1909. But Notre Dame survived both world wars, and its bells rang out to celebrate the end of the First World War and the liberation of Paris in 1944 during the Second World War. It is not just a building but a place extremely important in terms of collective memory and identity.
This is not the first time the glorious specimen of Gothic architecture has suffered a tragedy and needs serious restoration. With a long winding history comes the wear and tear. The famous gargoyles and the spire were in fact restored as late as the 19th century.
Considering the importance of the structure in French and world history, President Emmanuel Macron has promised to rebuild. The weight of restoring history lies in maintaining an honest bond with the truth. One must only create what existed in its purest form. To be true to what existed, one must know intimately the structures and spires, Andrew Tallon, an architectural historian performed an exact digital reconstruction of Notre Dame in 2015. Tallon used laser scanners to capture the entirety of the cathedral’s interior and exterior in point clouds. In a short video documentary for National Geographic, Andrew Tallon first explained the process. He started work on creating digital models for the cathedral to answer one simple question: How did they do it? It is a complex building with stone, wood, and glass. Victor Hugo, the writer of “The Hunchback of Notre-Dame” , referred to the building in its title as a“symphony in stone”.
Case Study 2: Restoring the war torn lands of Syria
The 2,000-year-old city of Palmyra was once Syria’s most popular tourist attraction. Walking through the Roman Great Colonnade to the Temple of Bel, with the sun setting and the stones turning gold and pink in the desert light, you felt a deep connection across the centuries to the city’s heyday.
Russian researchers had created a model of the ancient city of Palmyra, using photogrammetry on thousands of drone images. The 3D model was created by scientists from the Institute for the History of Material Culture of the Russian Academy of Sciences, with the help of experts from the Hermitage Museum. As part of their work on the project, which features both landscape and architectural designs of Palmyra, Russian researchers visited the Syrian city in September 2016. During their special expedition, some 20,000 drone images were taken.
This remarkable new capability — to rebuild exact copies of urban structures — goes much further. From Palmyra to the Iraqi city of Mosul and the Nepalese capital Kathmandu, new technologies in digital copying and 3D building are allowing us to bring back not just monuments, but entire cities from the rubble.
Point Clouds and the value of measurements:
First step in the process of recreation is analysing the creation itself
Here are some images from the point clouds created by Andrew to shed light on the structural complexity of Notre Dame. The accurate measurements from the models show that the central pillars bend outwards as they go higher, a fact we might not have known otherwise.
Some key advantages of this approach are: formation of a dense point cloud which can create full texture models, go beyond the limitations of two dimensional data to create a highly visual models integrable with BIM (Building Information Modelling), Agisoft, AutoCAD Revit, and Modelspace. The intention is to not only prepare highly detailed models but study the relationships between parameters and the delta of change a structure witnesses with time. Although, money for reconstruction is not a bottleneck in this case, but these methods can massively optimise the operational costs.
3D reconstruction of physical structures allows humans another way to experience history and be true to it. Indeed, we need not stop at monuments, our modern day cities and villages would benefit from the robust planning based on this data. With 3D data, we are preparing for posterity.
