How a 3d model helps the restoration of the kolner cathedral

How a 3D model helps the restoration of the Kolner Cathedral

Gothic sculptures are complex as compared to modern components, keub peter fussenich. The kolner cathedral manager continues with his team’s craft traditions, which are required elsewhere. For this reason, UNESCO has started working on the dom into the intangible world heritage site. The substance of the kolner cathedral with freestanding struts, strivebow, gothic ornamental tower, the fiaighers, and the eyelashes mentioned gothic mobility gables is partly 700 years old. In particular, the medieval components must be carefully monitored.

Since 2017 mapping the cathedral-master damage, stone species and other properties on the kolner dom digital. In monument preservation, the cathedral foresteister set the program metigo map from the company fokus leipzig. So far, they were able to mercy the damage but only two-dimensional mapping. Since 2021, three-dimensional is mapped. This has the advantage that damaged places can be considered from any angle.

Three-dimensional mapping

Together with the leipzig manufacturer and the company northdocks from the north rhine-westfalische monheim am rhein develop the dombekreiser metigo map for the purpose of three-dimensional mapping. A central component is the monitoring with the help of drones. Northdocks has initially divided the entire cathedral into traversable and predictable units such as choir, west facade and tower. Over a period of several years, the entire building will be photographed with the drones. This creates a detailed 3D model of the cathedral.

First, there was concerns whether it was indeed possible to accomplish the building with drones exactly. Again and again the cathedral-border drones of hobby airlines in the stoves, because on the kolner dom complex wind situations result from his position in the city and its structure. In a test on the north tower northdocks can prove that you can quite sure the cathedral.

How a 3D model helps the restoration of the Kolner Cathedral

With DJI-M300 drones, the company northdocks is designed to photograph the kolner cathedral to photograph the facade high uprich.

The 3D cathedral

The model consists of a polygonnet, which is textured with the photos. In addition, it contains data based on the documents and tarpaulins. With virtual reality headsets, the finished 3D model is experienced. The mapping of the cathedral goes into a crucial phase this year: in the third quarter 2021 northdocks had the entire building worn and the data has evaluated. Currently the chorus is recorded. The cathedral is partially involved and then parts of the rust also land in the 3D model. Since the finished model should be rustless, model parts are repeatedly replaced.

On each flight day arises about a terabyte photo material. Overall, hundred thousand 60 megapixel photos have been created so far. In such many photos it’s hard to true that all pictures have the same quality. Northdocks photographed in RAW format because massive color and image corrections are upgrading to get a homogeneous image without shadows. "We have developed our image and distortion corrections ourselves. In addition, we sort pictures according to sharp criteria. If the drone has moved through a windstob and to see motion creatures in the photo, it does not come to the model", reports joachim perschbacher, business drivers and technical director of northdocks.

Billions of polygons

In the end, a model of two billion polygons should be created from the data material. The texture trigger is currently 216K, about 216.000 pixels in width. According to northdocks, this corresponds to a real resolution of less than a millimeter. Some corners are currently inaccessible for the drone airfields; there is the resolution lower. The complexity of the 3D model will still increase over time when the drone flyers penetrate deeper into the streb, suspects perschbacher.

The drones are repeatedly replaced by new models. Currently, northdocks flies with a drone of the type DJI M300. Including batteries weighs the drone 6.3 kilograms. In addition, she can wear 2.7 kilograms. All photos are created with the same camera type. Cameras of the sony alpha series are used with sigma lenses, which map with relatively low distortion.

For photogrammetry, nothdocks uses the realitycapture program, software that creates 3D models from disordered photos. The software was currently purchased from the gaming company and game engine developer epic games, taking photogrammetry in game development is becoming increasingly important. "For the kolner cathedral realitycapture is based on the iterative process for us best tool", says perschbacher. "We have already worked with agisoft metashape. But that works slower for our application." the complete model to calculate duration with the currently used proceedings about a week.

How a 3D model helps the restoration of the Kolner Cathedral

The model archives the current state of the kolner cathedral for the future.

WOFUR the model serves

First and foremost, the 3D model should support the cathedral boomister at the preservation. At today’s state of the model, the 175-meter high tower can be fully departed in virtual reality. There is a VR glasses of the type HTC vive pro. The software also supports the models HP RBBL G2, oculus rift S, oculus quest and pico. The domain master can not see damage that you can not see with blobem eye and can not reach with cranes. On the basis of the model you can decide which stones use the stonemases and order them already in the quarry. This is an organizational advantage and saves time.

For example, northdocks has recorded a decorative water pier three-dimensional, which now serves as a template for the sculptor. The 3D model facilitates and accelerates the work. The sculptor can focus on craftsmanship in a different way than that was possible 50, 100 or 500 years possible. "We already know for decades where we want to put rusty", says dombaumister fussenich. "In the 3D model, we recognize details that we have else we first detected when the rust is."

The project is designed for long-term monitoring. In the course of course, the DOM should be monitored automatically by providing the drones largely autonomously the tower when there is a damage there. For this, the necessary map material already exists.

An important side effect is a digital archiving of the entire building, all considering all those involved in the project in the face of the brand of the notre dame cathedral in paris for.

Beyond the treeonitoring you can make more with the model. "For example, we can simulate certain weather conditions that rarely occur", explains northdock business drivers perschbacher. "For the fire department we can simulate missions, and for tourism we can offer perspectives of the cathedral that were not possible in the reality." A resolution reduced version of the model with about 100.000 polygons has also been running on smartphones and tablets. A virtual tour of the kolner cathedral has already created the WDR.

How a 3D model helps the restoration of the Kolner Cathedral

The cathedral champion can discover damage on the model in virtual reality and plan repairs.

New insights

Next to the kolner cathedral northdocks also mapped chemical plants. For industrial plants, many structures like pipelines are repeated. In the DOM, however, no component is similar to the other, even if a tower looks like the other. "There are angel figures on uber 100 meters, which are not directed to the outside, but ranging to the cathedral where they can not see a human being", staunt perschbacher.

Thus, it does not matter if you are credible or not. The kolner cathedral impresses with the dedication of the master masters who have shaped him over centuries. In the 3D model, this attendance will be experienced. Dombekister peter fussenich supplements: "thus, the drones have recognized that the cathedral is built for the eye of god."

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