Immersive Digital Restoration Transports Visitors to 17th-Century French Fortress

Reality capture technology from Leica Geosystems, part of Hexagon, digitally preserves France’s 17th century Citadelle de Besançon.

Rising high above the city of Besançon in eastern France, the 17th-century Citadelle de Besançon stands with its weathered walls containing over 400 years of rich history. Built by military architect Sébastien Le Prestre de Vauban, the Citadelle is perched atop Mount Saint-Étienne and sprawls over four hectares. This UNESCO World Heritage Site has endured wars, sieges, and the ravages of time. Today, it houses four museums, including a zoological park.

An innovative technology project, sponsored by the French Government, is underway to bring the historic Citadelle to life while preserving its legacy for future generations. The project uses reality capture technology from Leica Geosystems, part of Hexagon, to create a comprehensive 3D model of the entire Citadelle.

Leading the effort is Hugo Parent, the head of the heritage department at the consulting firm Capture4Cad. Parent’s expertise in this field and his previous experience in scanning sections of the Citadelle make him well-suited to oversee the project. The commission was issued by the French Minister of Culture, with the goal of creating a 3D model of the entire 17th-century Citadelle. The project aims to create an augmented reality version of the 17th-century Citadelle for visitors to experience, while also using the data to preserve the UNESCO World Heritage site.

The challenges of scanning 17th-century history

The task of digitally capturing the Citadelle presented significant challenges due to the site’s size and complexity. Parts of the Citadelle, such as cliffs and high walls, are inaccessible to people, making preservation of the already crumbling site difficult. Yet to bring the site to life in a virtual environment requires precise 3D laser scanning to be conducted on the ground, from the air, through tunnels, and down a 128-meter well. Along with the physical challenges of scanning the site, capturing had to be scheduled around visitor access hours and carefully coordinated to avoid disturbing the animals from the nearby zoo.

Precision was made possible using technology from the Leica Geosystems’ BLK autonomous reality capture portfolio of 3D laser scanners to create a comprehensive 3D model of the massive structure. Digitalizing the Citadelle will help preserve it and enable more visitors to experience its history through augmented reality.

Using a range of BLK laser scanners, Capture4Cad was able to cover the whole site within a tight timeframe. The Leica BLK2FLY autonomous flying scanner captured the towering ramparts, sheer cliffs, roofs, and facades of the citadel. The Leica BLK ARC, an autonomous laser scanning module for robots and mobile carriers, was mounted to Boston Dynamics’ robotic carrier. This enabled the team to lower the technology 128 meters into France’s deepest well to thoroughly scan the well shaft. In the underground tunnels, the handheld Leica BLK2GO laser scanner provided uninterrupted scanning on the move. 

“The range of Leica BLK autonomous scanners was essential to create the reality capture model of this expansive and intricate site,” said Hugo Parent. “From capturing the point clouds to generating the 3D model, we relied on Leica Geosystems technology to bring all the elements of this project together.”

Once the scans are complete, the team uploaded them to HxDR, a cloud-native digital reality platform from Hexagon. It supports and scales geospatial data, connecting the data captured throughout the Citadelle to create a cloud-based model of the entire structure, both above and below ground. The model will be used to create an augmented reality experience, enabling more visitors to explore the site through their preferred devices.

According to Leica Geosystems’ Giuseppe Mazzara, director of sales development, autonomous reality capture, “This ambitious project highlights how autonomous scanning solutions are able to access and capture complex sites as well as process huge amounts of data. We are proud to play a part in telling the Citadelle de Besançon’s rich 400-year history and preserving it for future generations.”VIDEO: https://www.youtube.com/watch?v=27UhoSOWpl4