Building the digital twin of St Peter’s Basilica in Vatican City

St Peter’s Basilica in Vatican City is one of the holiest sites in the Roman Catholic Church. Designed by Michaelangelo and Gian Lorenzo Bernini and constructed over more than a century, it is one of the Seven Pilgrim Churches of Rome. The Basilica draws tens of thousands of pilgrims and tourists each year. The Fabric of Saint Peter (the arm of the Church responsible for the conservation and maintenance of the Basilica) appointed Italferr to develop a digital twin of the Basilica ahead of the Vatican Jubilee celebrations in 2025.

Italferr was tasked with mapping and analysing every building element for constant structural monitoring. The project had two main objectives: to create a digital twin with all the information accumulated over the centuries about the Basilica; and to implement a monitoring system using digital methods and applications to ensure the protection of the Basilica.

The historical and religious significance of this structure meant that Italferr needed to ensure the digital twin of the Basilica was as accurate as possible. However, it required an extensive survey. To achieve its goal, Italferr’s first step was to conduct a geometric survey of the forepart. As it was built in the 1600s, it must be closely monitored for signs of deterioration or damage.

Daniela Aprea, director of technology, innovation, digital spoke and digital rail infrastructure development at Italferr, said: “The goal of this phase was to reconstruct a digital model using point clouds and photos to determine the dimensions of key architectural and structural elements and gain information about what is not accessible [using traditional surveying methods].”

However, this process produced a large amount of data that needed to be managed and processed into a reality mesh, and shared among multiple disciplines and stakeholders for continued monitoring. By the end of this phase, the team had acquired more than 3TB of data for an area of 65,000 sq m in plan and 240,000 sq m of vertical surfaces. Therefore, to address these data management challenges within a six-month timeline, Italferr needed integrated and open 3D modelling and digital twin technology.

Already familiar with Bentley applications, Italferr chose ProjectWise, iTwin Capture Modeler (formerly ContextCapture), and MicroStation to manage the multi-sourced data and generate a digital twin shared among 30 people.

To manage the large amount of data and encourage sharing and collaboration, the team used ProjectWise to create a data-sharing and collaboration platform accessible to all project stakeholders. Users of the platform could access survey data, as well as geometric, informational, and analytical models. “ProjectWise was functionally structured for use, with workflows and transitions between different states, supported by weekly coordination meetings and reviews. Each participant had logins and privileges to ensure that operations were tracked, and that the necessary information was available for their role in the project,” explained Aprea.

Once the information was housed in one place, Italferr processed and managed point clouds through iTwin Capture Modeler. The team created a fully navigable 3D model with the correct scale and proportions, measurable by linear lengths, surfaces and volumes. The 3D model was also georeferenced with the same system used by common mobile devices for geolocation.

“With the use of iTwin, the foundation was laid for the implementation of the digital twin,” said Aprea. By taking the data sources housed in ProjectWise’s central location and combining it with the single reality mesh, the team could create a digital twin to both view and make changes in real-time. The team could also create specific models to be shared across multimedia platforms.

“The creation of the digital twin required an extensive survey campaign using cutting-edge technologies, such as topography, laser scanning, aerial photogrammetry using drones, and georadar,” said Aprea. “With these capabilities, it was possible to create a complete model of the work, considering that due to its history, exhaustive drawings of the Basilica were not available, with all information regarding the rooms, elevations, wall thicknesses, floors and vaults.”

By working in a collaborative digital environment, Italferr saved 50 hours in modelling time, delivering the model 20 days ahead of schedule to the Fabric of Saint Peter. The team estimates that by going digital, it saved 200 hours on the project.

“The implementation of the digital twin of St Peter’s Basilica was a challenging project both in terms of time and complexity. The use of Bentley’s solutions made it possible to optimise not only the sharing and collaboration processes, but also the modelling processes,” said Aprea.

Using a digital twin proved a more efficient way to share information with stakeholders, increasing data-sharing efficiency by 75% compared with traditional sharing applications. It also reduced the number of onsite visits by 75%, letting stakeholders view the survey without leaving their offices.

But perhaps more importantly, this digital twin serves as unique information technology that will showcase the structure’s past, present and future. It will allow the Fabric of Saint Peter to monitor and maintain the landmark site for years to come.

“Through the use of advanced algorithms, it will be possible to analyse the response of the structure to static and dynamic stresses, obtain in-depth knowledge of the health of the structures, and develop a permanent structural monitoring system,” said Aprea. “The implementation of a structural monitoring system for St Peter’s Basilica is of extraordinary value not only in terms of engineering, but also in social terms, as it will make it possible to preserve in the decades to come the full functionality of the work that is the centrepiece of the Christian faith throughout the world.”

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