The illuminated cathedral

Experts and the Dombauhütte have scanned the “Steffl” with 21 billion laser points – for building analysis, damage documentation and simulation of historical building conditions and, more recently, also for art

As part of a research project, Vienna’s St. Stephen’s Cathedral is being completely scanned with billions of laser points. The virtual rendering is intended to help with preservation, but is also part of an art project. Regular, complete and, above all, accurate surveys of historically significant buildings are desirable both for ongoing conservation measures and for complete long-term documentation. Traditional methods for creating as-built plans were generally time-consuming and expensive.

In 2018/19, St. Stephen’s Cathedral was completely surveyed within a few working days using a 3D laser scanner. This made it possible for the Dombauhütte in particular to create any views and sections of the building at any time. These are used for building analysis, as a basis for ongoing damage documentation and for the simulation of historical building conditions.

Anyone who wants to marvel at the impressive architecture of the “Steffl” no longer necessarily has to be on site: In the project “The Translucent St. Stephen’s Cathedral”, 3D data enables a virtual interactive tour where visitors can explore defined points of a rendered point cloud. The Austrian laser scanner manufacturer Riegl has created 21 billion laser points. This level of detail is actually used for building analysis, but in this case also for art.

It enables an extraordinary view of St. Stephen’s Cathedral in Vienna with several levels of transparency. The project was shown for the first time at the Ars Electronica Festival in September. The insights into the levels of the cathedral were created as part of the EU-funded “Immersify” research and development project. However, Riegl has been working with St. Stephen’s Cathedral for years.

The common goal is to precisely record and document the building fabric using 3D laser scanning – in the church interior, in the catacombs, in the attic and on St. Stephen’s Square. The point cloud data can be used to create precise detailed plans as well as views and sections, which are used by the Dombauhütte for building analysis, damage documentation and simulation of historical building conditions.

Nikolaus Studnicka from Riegl explains: “In the typical workflow with the terrestrial scanner, one so-called panoramic scan is taken after the other. An average of 22.5 million measuring points are recorded in 45 seconds during a full scanner rotation. The spatial resolution is around seven millimetres at a distance of ten meters.”