For the as-built documentation, investigation, and virtual realisation of this small but worthwhile Romanesque church from the 12th century, the ArcTron Group (Altenthann) team of 3D historic preservation specialists utilised cutting-edge aerial and terrestrial architectural surveying and 3D-modelling technology. The work, self-funded by ArcTron 3D, was primarily done as a part of the several months long internships of Melanie Nguyen (Building Research) and Fatih Sönmez (Multimedia) with support from the various experts at ArcTron 3D. The majority of the project was executed between April and September 2020 as a result of the pandemic and its subsequent restrictions, which made it necessary to come up with alternative ideas for internship projects. The St. Ägidius church is a small architectural highlight for historic preservation near the company headquarters. Normally, visitors are not permitted inside the church. However, with this digital visualisation, the doors are now “open” to everybody. We would especially like to thank Mayor Herrmann (Altenthann) and Pastor Lehnen (Brennberg) for allowing us to perform an on-site documentation of the church and present it digitally. We would also like to thank Mr. Domagala of the "Deutschen Stiftung Denkmalschutz" ("The German Foundation for Memorial Preservation") for admitting our project to the "virtual" Memorial Open House Day on the 13th of September, 2020!
First, the surrounding area of Schönfeld was examined and photographed from the air with the company’s ultra-light paragliding trike, in order to later construct a photogrammetric model. Back on the ground, the church was recorded from a variety of angles using drones, forming the basis for a model of the exterior. The next step was the precise documentation of the building’s geometry; using the terrestrial laser scanner, detailed point clouds were captured from a total of 87 positions in and around the building, including every room of the interior. The interior of the nave was photographed with a drone in order to properly document the high vaults of the ceiling. Finally, every interior room of the church was documented using the Structure-from-Motion photogrammetry to provide the point clouds with additional details and colour information. In this photogrammetric technique, many overlapping photos of an area are taken from different perspectives and later combined to calculate a realistic model of the spatial geometry.
The 87 laser scans were then combined into a point cloud containing over 100 million points, making the entirety of the church’s scanned interior and exterior geometry visible as one unified object. In the next step, the laser scans and all interior and exterior photos of the church were loaded into the program Reality Capture, of which ArcTron is a licensed retailer, where they were subsequently aligned with a large point cloud using the help of “tie points”. After further adjustment of the point cloud, it was used to generate a high-resolution mesh, which was then unwrapped (projected onto a 2D surface) so that its surfaces could be photorealistically retextured with the photographs taken on-site. An additional 3D model, this time of the hamlet of Schönfeld, was constructed using the same method and the photos from the flyover with the ultra-light paragliding trike.
In order to optimize performance and make the model more accessible and interactive for digital visitors, a pared-down, so-called “low-poly” model of the church was created. This way, it can also be used in future projects with VR (virtual reality) and AR (augmented reality) applications or computer games.
Next, the extremely high-resolution “high-poly” model generated in Reality Capture was imported into the 3D modelling software Maya so it could be replicated in a lower-resolution “low-poly” style. To ensure that the dimensions of the new model remained accurate, it was adjusted while referencing the original from multiple perspectives. Remodelling is done in a top-down fashion: beginning with the biggest and most noticeable elements, and then gradually going into finer detail. The exterior shape of the church was modelled in this fashion first, including the façade, entrance stairs, and roof with its ridge turret. Later, the interior rooms¬—the basement, attic, interior staircases, and the nave and gallery—were remodelled and individually aligned with their respective objects. After the finished reconstruction of the individual interior rooms, they were combined and integrated into the model of the church’s exterior.
To texture the new model, so-called “UV maps” were created of the individual 3D objects by dividing their surfaces into two-dimensional pieces and arranging them on a flat plane with the help of projections. This process is referred to as “unwrapping”. During unwrapping, it is important to make sure that the surfaces are not being unwrapped in a way that will create distortions or gaps in their new textures. The creation of UV maps is a key interim process for the assignment of materials and textures after a model has been finalized. The more precise the UV mapping is, the better the texture will “sit” on the object and the more realistic it will appear.
The surface or “skin” of an object, whose quality and resolution determine the realism of an object’s appearance, is referred to as its texture. Consequently, high-resolution, photorealistic textures are particularly important when it comes to historic preservation! A surface can have multiple different textures, such as spots of rust or dust on a piece of metal or wood, which make the object appear more realistic. In general, two types of textures can be distinguished, both of which were used in the model of St. Ägidius: finished textures from external sources and “baked” textures taken from the original photogrammetric model. Alongside these are also “assistance textures”, referred to as maps, which contain specific information and can be combined with the two main texture types, ex. to give the appearance of depth on a flat model surface. Such a map can be generated with depth information, which is either already included in the scan mesh, or can be created in a special image editing software. Außerdem gibt es noch „Hilfstexturen“, sogenannte „Maps“, die mit den beiden Haupttexturarten kombiniert werden können, beispielsweise um einen Tiefeneindruck auf einer geraden Modelloberfläche zu erzeugen. So eine „Map“ kann mithilfe von Tiefeninformationen generiert werden, welche entweder bereits in den Scans enthalten sind, oder mithilfe einer Bildbearbeitungssoftware erzeugt werden.
With the help of PBR (physically-based rendering) material assignment, a texture can simulate the interaction of light with materials such as metal, wood, plastic, glass, stone, etc. Additionally, one object can have multiple materials, which then react differently to incidences of light depending on the circumstances. A variety of 3D platforms and game engines allow the combination of “assistance textures” like normal maps with a regular texture in order to get as close to reality or the desired look as possible.
Have a look at our interactive 3D model for a quick, photorealistic trip around the building and into its otherwise inaccessible interior!
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