Imagine you could travel through time and experience one of the most impressive monuments of Roman history up close. Wouldn't it be fascinating to explore the Heidentor from the 4th century right from your home? Thanks to modern 3D technology, this is now possible. Join us in the making-of to take a look behind the scenes at the 3D digitisation process.

Using a drone, a current image of the Heidentor as it appears today was captured. The drone takes high-resolution photos from various perspectives and heights, which are then compiled into a comprehensive 3D model on the computer. This technique, known as “photogrammetry”, requires advanced technology and significant expertise.

Afterwards, three additional models were natively created in 3D on the computer, depicting views of the Heidentor from different eras. This allows for a fascinating comparison between how the Heidentor looks today and how it might have looked in the past.

Several 3D models of the Heidentor can be found in Kulturpool:

• The Heidentor of Petronell-Carnuntum – the modern-day view of the Heidentor
• Reconstruction of the Heidentor – the Heidentor as it was almost 2,000 years ago
• The Heidentor in the early 19th century – historical reconstruction
• The Heidentor in the late 19th century – historical reconstruction

In 3D digitisation, there are various roles within the team:

Curators (such as historians and archaeologists) are responsible for the selection and contextualisation of the objects. They possess the necessary expertise and narrate the object's story through accompanying texts or annotations within the 3D model.

Photogrammetry experts handle the photographic capture and later data processing and should also operate the drone for aerial photography.

Graphic designers create the 3D model. This requires specialised visualisation expertise in 3D modelling.

Finally, someone with digitisation expertise is needed to make the final product available to the public on an online platform.

Photogrammetry digitisation requires specific technical equipment and software.

Camera & lenses: A high-resolution DSLR or mirrorless camera is ideal. Wide-angle lenses work well for capturing large objects and panoramas. A robust tripod is also recommended.

Drone: For aerial shots of large or hard-to-reach monuments, a drone with a high-quality camera is the preferred choice.

Measuring tools: Laser distance meters or similar measuring devices are useful for measuring distances and dimensions.

Photogrammetry software: Specialised software is needed to create the 3D model from the individual photos. For the Heidentor model, Reality Capture was used. Blender was utilised for post-processing and creating the historical models.

Computer & storage: Photogrammetry requires powerful computers with strong graphics cards and plenty of RAM, as well as sufficient internal and external storage space for backups.

GPS device: GPS devices can be helpful for georeferencing and location determination.

The DJI Mavic 3 Enterprise drone was chosen for the Heidentor project due to its high-resolution camera, light weight, and easy operation. This drone also allows for centimetre-accurate mapping.

Significant preparation is needed before the first flight of the drone, varying according to different national laws. The drone pilot must have an appropriate drone licence. In Austria, drone liability insurance is compulsory. Using the insurance number, the drone is registered digitally with the Austrian aviation agency Austro Control (dronespace.at). This registration number must be affixed to the drone. Finally, the drone is registered with the drone manufacturer.

Drones are subject to flight restrictions set by Austro Control. It is prohibited to fly near airports and their control zones, hospital helipads, and military installations. Depending on the drone's take-off weight, flying over uninvolved people may be restricted. Flight restriction zones are shown on certain online maps.

For the photogrammetric capture of the Heidentor, appropriate weather conditions were the basic prerequisite to achieve the best possible result. It was necessary to wait several weeks for cloudy but not rainy weather. Rain is not good for the drone, and the sun casts shadows that would later be visible in the 3D model, which is not ideal. Cloudy weather, on the other hand, provides the right diffuse light.

One day, the conditions were finally perfect, and the drone could take off for the first time. The captures were successfully completed within one morning.

The first results of the 3D model were available after two days. In the following weeks, annotations were prepared, allowing the location of ancient spolia in the Heidentor. Additionally, a human figure was recorded in a studio and implemented into the 3D model to better illustrate the proportions.

In total, the digitisation of the Heidentor, from planning to the digital twin, took about six weeks. This short time frame was only achievable thanks to experienced professionals.