Preserving historic St. Peter’s Basilica with a digital twin

A leading Italian engineering firm took on a pioneering surveying endeavour: to map the iconic St. Peter’s Basilica in Vatican City. Commissioned to create a digital twin of the revered structure, the firm utilized advanced geospatial mapping techniques to meticulously capture every architectural detail. This article provides an in-depth exploration of the project, highlighting the fusion of innovative surveying technology with historical preservation.

St. Peter’s Basilica is one of the world’s most significant architectural and historical structures, serving as one of the holiest Catholic shrines and attracting tens of thousands of pilgrims and tourists annually. Designed by Michelangelo and Gian Lorenzo Bernini, the basilica took more than a century to construct and is renowned for its Italian Renaissance and Baroque architecture. It holds the distinction of being the largest church in the world by interior volume. Since the early Christian period, many popes have been interred there, and it is one of the Seven Pilgrim Churches of Rome.

The Italian engineering firm Italferr was commissioned by the Fabric of Saint Peter – an institution of the Roman Catholic Church responsible for conserving the basilica – to create a digital twin of the structure. This may seem an unexpected match, as the company is primarily known for projects to scan transportation infrastructure such as railways and bridges rather than for heritage mapping.

The company was tasked with meticulously mapping and analysing every element of the building for continuous structural monitoring ahead of the upcoming jubilee celebrations in 2025. The project had two main objectives: to create a digital twin with comprehensive information about the basilica, and to implement a monitoring system using digital methods and applications to protect the structure during ongoing renovation and restoration projects leading up to the Jubilee 2025. In the Catholic Church, a Jubilee or Holy Year is a special period declared by a pope to allow the faithful to benefit additionally from the spiritual treasures of the Church.

Structural monitoring system

The digital twin project was initiated to preserve this unique architectural and religious heritage for the world. Through the use of advanced algorithms, the project aimed to analyse the structure’s response to static and dynamic stresses, gain in-depth knowledge of its structural health, and develop a permanent structural monitoring system. Data from the sensor network would be integrated into the digital twin, and the processed information would be shared with the Fabric of Saint Peter for future maintenance and management of the basilica.

The historical and religious significance of St. Peter’s Basilica required the digital twin to be as accurate as possible, necessitating an extensive survey campaign. Italferr’s first step was to conduct a geometric survey of the forepart, built in the 1600s, which must be closely monitored for signs of deterioration or damage.

The creation of the digital twin involved an extensive survey campaign using advanced mapping technologies, including topography, laser scanning, aerial photogrammetry using drones, and georadar. Due to the lack of exhaustive drawings of the basilica, these mapping methods were crucial in creating a complete model of the structure, including information about the rooms, elevations, wall thicknesses, floors and vaults.

Terabytes of data

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 obtain information not accessible with traditional surveying methods. However, this process resulted in a large amount of data that needed to be managed and processed into a reality mesh, as well as shared among multiple disciplines and stakeholders for continued monitoring. By the end of this phase, the team had acquired over 3.1TB of data for an area of 65,000m² in plan and 240,000m² of vertical surfaces. To address these data management challenges within a six-month timeline, Italferr needed integrated and open 3D modelling and digital twin technology.

Over the following two months, both internal and external teams – employing drones and an aerostatic balloon – flew inside the basilica. They acquired all the necessary information without risking damage to the extremely precious building, capturing more than 15,000 photos (equivalent to 630 gigapixels of data). Subsequently, extensive data processing occurred over two months, facilitated by multiple processors operating in parallel, to develop the building information model (BIM) and digital twin of St. Peter’s Basilica. The use of advanced geospatial software solutions facilitated this process.

Towards a 3D model

The firm went on a quest for software capable of converting reality data into real-world insights for high-quality 3D modelling, and ultimately digital twins to facilitate informed decisions for cultural heritage maintenance. For this purpose, Italferr chose to utilize various Bentley software solutions, including ProjectWise, iTwin Capture Modeler (formerly widely known as ContextCapture), and MicroStation. These software tools were employed to manage multisourced data and generate a digital twin shared among 30 people.

To manage the large volume of data and promote sharing and collaboration, the team utilized ProjectWise to establish a data sharing and collaboration platform accessible to all project stakeholders. This platform allowed users to access survey data as well as geometric, informational and analytical models. The software was structured for practical use, featuring workflows and transitions between different states, supported by weekly coordination meetings and reviews. Each participant had their own login and privileges to track operations and ensure that necessary information was available in line with their role in the project.

Once all the information was centralized, the next step was processing and managing point clouds. 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. Subsequently, the 3D modelling software laid the foundation for the implementation of the digital twin. By combining data sources housed in a central location with a single reality mesh, the team created a digital twin for real-time viewing and modification. They also created specific models that could be shared across multimedia platforms.

The advancements of going digital

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

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

According to the surveying crew that conducted this special project, using a digital twin proved to be a more efficient way to share information with stakeholders, increasing data sharing efficiency by 75% compared to traditional sharing applications. It also reduced on-site visits by 75%, allowing stakeholders to 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. Moreover, the implementation of a structural monitoring system for St. Peter’s Basilica – the centrepiece of the Christian faith throughout the world – is not only of extraordinary value in terms of engineering, but also in social terms. It will make it possible to preserve the full functionality of the basilica in the decades to come.

The creation of this digital twin has led to several notable uses. Primarily, the project aimed to establish a comprehensive digital record of the basilica. An important application is that real-time data from Internet of Things (IoT) sensors, including tiltmeters and accelerometers, is being utilized to prepare for restoration work. Besides the teams of engineers, designers and contractors who will rely on the digital twin in their work to preserve and protect the basilica, there are other audiences for the immersive digital model. For example, digital twins and reality capture can also be valuable tools for education. The model has tremendous applications for post-secondary students, academics and researchers of art history, architecture and engineering.

Conclusion

While it is true that reconstruction and maintenance work in historical buildings require detailed and accurate information, acquiring such data efficiently can be difficult and expensive. However, advancing methods of reality capture, as well as measuring and monitoring structures and surfaces, are making these tasks less complicated and time-consuming than in the pre-digital era.

The surveying and monitoring project of St. Peter’s Basilica in Vatican City presents a great example of the power of geospatial technology in preserving cultural heritage. With the objectives of creating a digital twin enriched with centuries of accumulated information and implementing a robust monitoring system, remarkable results were achieved. The digital twin of the basilica is set to serve as a crucial resource for safeguarding this unique heritage for future generations. Leveraging high-end geospatial data and the right software not only saved valuable time, but also enhanced the efficiency. As a result, the model was delivered ahead of schedule with a significantly reduced need for on-site visits. This project underscores the importance of interdisciplinary collaboration and the vital role of geospatial data in protecting and preserving our cultural treasures.

Acknowledgment

Some of this content is based on an article titled ‘Italferr bewahrt den historischen Petersdom mit einem digitalen Zwilling,’ previously published (in the German language) in gis.Business, a German magazine for geoinformation and geo-IT.