5G enables the preservation of Cologne Cathedral with digital twins

In 2020 the west facade of Cologne Cathedral was captured for a realistic 3D visualisation using drone-based technology. The recordings were intended to help the employees of the Dombauhütte (responsible for the preservation of the cathedral) to better monitor areas of the building that are difficult to access and to detect damage at an early stage.

Previously examining complex structures such as Cologne Cathedral for damage required the erection of complex scaffolding, which is a lengthy and expensive task. However, drones have been increasingly used at the cathedral with the first test recordings with unmanned flying drones from Northdocks made in the autumn of 2019.

As an unexpected benefit of the Coronavirus pandemic, Dombauhütte Cologne took advantage of the fact that the immediate area around the cathedral was far less frequented than usual due to the pandemic regulations of the city of Cologne. "This makes it possible to block off a small part of the cathedral platform in front of the west facade of the cathedral so that the drone pilots can concentrate on working on the cathedral towers from there," said Michael Jürkel, stone technician at the Cologne Cathedral workshop. Pilots carefully guided the drone at a distance of five to seven meters along walls, towers, peaks, ornaments and figures – sometimes to where no one had been for a century and a half.

To support the creation of a digital twin of Cologne Cathedral Northdocks pilots undertook over 350 of hours pure flight time. A high level of precision and concentration is required since the more attentively pilots can control the drones fitted with high-resolution cameras, the lower the post-processing overhead and the greater the benefit for the stone technicians who will ultimately use the digital twin, since the resulting 3D model allows more precise mapping of damage. As part of the work, the manually controlled special drone covered the towers and west facade of the cathedral in more than 400,000 high-resolution images ultimately combined into a 50GB data model. With 35 billion polygons, the virtual twin of bits and bytes looks as real to the viewer as the original building made of stone. As of today, Northdocks has captured and processed the complete cathedral from the outside as well as the most significant indoor areas using a combination of drones, laser scanning and handheld cameras.

Now everyone who wears VR glasses to view the digital twin thinks they are standing in front of the building at an astonishing height. The technology can deliver a very detailed and accurate replica of the original building allowing cathedral employees to spot even the smallest restoration needs based on the detailed digital twin. It can also support an enhanced viewing experience for tourists, extending to untouched and usually inaccessible spaces. Ultimately, this may help the future tasks of general maintenance workers, fire inspectors and firefighters as the digital twin would help in the identification of critical areas.

For the deployment of the digital twin of Cologne Cathedral, Northdocks adopted Vodafone’s 5G Edge solution combined with AWS Wavelength. In combination these technologies better enabled the company to handle significant data volumes, while enabling the company to provide more and better real time data, statistics and analysis for remote employees.

With higher bandwidth 5G connectivity and local processing supported by MEC the digital twin can be rendered remotely, while still displaying even the smallest of details at across the cathedral. The full value of digital twin data can only be unlocked when it is highly accurate, precise, and timely, so underlining the advantages of 5G and MEC.

A particular benefit is that the Cologne Cathedral project makes use of public 5G cellular networks for connectivity, allowing for flexibility in deployment of this and future projects; saving deployment time and cost and reducing complexity. Additionally, the use of public 5G networks allows on-site workers to access the digital twin of the cathedral more easily given the ready availability of high-speed connectivity services. In particular, when viewing a digital twin, 5G is critical in reducing lag that may be apparent with previous cellular generations. Even small lags between user movements and the movement of a VR image can very quickly make those users feel nauseous but the bandwidth and latencies supported by 5G and MEC allow for smooth interaction between users and the digital twin.

Since access to the digital twin technology relies on public 5G network connectivity, the digital twin of Cologne Cathedral can be viewed by anyone connected to the public 5G network. This allows for sophisticated hybrid working models, with different users in different geographic locations able to view and discuss the same images in real time. This flexibility further enhances the potential of the digital twin image to be used for training and sharing best-practices between stonemasons, including those working on the Cologne Cathedral project and those working on other renovation projects. In particular, the 5G-enabled access model allows for each escalation of any particularly complex renovation challenges to appropriate supervisors or simply more experienced stonemasons. Such escalation process can be quick, simple, and seamless.

The fact that users of the VR headsets are in fact viewing video feeds that have been generated remotely (rather than a local copy of the digital twin) allows the solution to be deployed with a minimum of on-site equipment, further increasing flexibility and reducing costs. This approach also enhances security, since any potentially sensitive information contained in a digital twin remains safely stored on cloud infrastructure with no local copies that could potentially represent a security risk. Meanwhile, any updates to the digital twin can be processed and implemented quickly and easily to the single shared digital twin, rather than requiring coordinated propagation across an estate of multiple local digital twins.

In cases where expert stonemasons and restoration workers need further information about a particular aspect of the cathedral as part of the ongoing works, this information can be gathered with drones and used to augment the existing digital twin information. Thus, the digital twin of Cologne Cathedral will become a living thing that is updated over time.

Beyond the restoration process, the gathered imagery can be used to support an enhanced visitor experience, allowing close-up viewing of walls, towers, peaks, ornaments and figures, and potentially from remote locations.

Additionally, the 5G-enabled approach to deploying digital twins as demonstrated by Northdocks with Cologne Cathedral is well suited to the use of digital twins of a range of industrial locations and complexes. This is particularly the case where site owners are sensitive to security and the potential for image information to be compromised. By its nature, the 5G-based solution used to support the digital twin of Cologne Cathedral does not require the storage of any 3D models on the mobile devices used in the field: information is transmitted directly to individual display devices via video feed only, while the 3D geometry remained safely on a central server PC. An alternative approach that does not use 5G would likely result in extensive geometry information being stored (at least temporarily) on mobile devices, sometimes overflowing their storage capacities while also creating potentially significant security risks.