This year, Douglas Pritchard began his journey to scan the largest building in the world in the 1800’s, Germany’s Cologne Cathedral. Although it is no longer the tallest building, the Cologne Cathedral still remains Northern Europe’s largest Gothic church. The job was no where close to easy for Pritchard, as many unique problems presented themselves along the way, but eventually he would prevail.
Some of the challenges Pritchard faced were due to the size and complexity of the cathedral. According to Pritchard,
.“It was difficult to be sure that as much surface area as possible is covered…The other thing is that it’s a Gothic cathedral—it’s not like a square box where you can scan from four different points in the building. When you have a highly articulated facade due to the Gothic architecture, you really want to take the scanner all over the place to capture as much detail as possible.”
The cathedral features two massive, detailed spired which stand at 515 feet tall each. “This is one of the reasons I wanted to scan the building,” Pritchard said. “Because of its height, you have to look at ways of positioning the scanner so that you could document as much as surface area as possible. You have to be innovative.”
In order to overcome these challenges, Pritchard was forced to get creative. He explains,
“I’ve been involved in a number of projects where I’ve been able to propose using rigs, extension arms, and even inverting the scanner…In the case of the gigantic cathedral towers, I was able to position the Z+F 5010X scanner vertically, and then invert the scanner, pointing it downwards at the 150-meter level. And there are these openings on the tower, so you can move the scanner in a clockwork pattern, pointing it up and then down. That worked quite well.”
Although this approach to scanning the entire surface was adequate, Pritchard still found that the colossal size of the cathedral still made the image processing difficult because he was taking about as many scans as his 3D software could handle. Hence, he was forced to get creative again, stating:
“I created smaller data sets that link…I’ve broken the scanner data down based on height, and if it’s interior or exterior. You have the two towers, obviously, but when you look into the chapel area and other parts of the cathedral there are very distinct levels. So there’s a 20 meter level, 27 meter level, and so on.”
Pritchard never fell short in his praising of the advances in 3D scanning technology which include the integration of HDR cameras. As Pritchard provides,
If I went there with a scanner that didn’t have an onboard camera, I think that would have been really unfortunate. I would have spent this massive effort to get the dimensional data, but no imagery…The cathedral has a very advanced conservation department. They’re looking at this as a way to document the facades of the building and identifying areas that need to be repaired or replaced.”
Imagery is crucial in the 3D scanning process. Pritchard elected to use a scanner very similar to the EvixScan 3D Scanner which includes four 5 megapixel cameras. Using a 360 degree camera to help supplement the scan data would have only made the process more difficult. Pritchard explained the importance of having a scanner like the EvixScan 3D Scanner,
“One of the reasons I chose the [scanner] was because of the HDR camera. That was particularly important when the scanner was either raised up very high, or extended outward off the facade of the cathedral. Having the camera plane and the laser at the same point meant I could remotely operate [it] as a scanner or a camera or both.”
The purpose behing Pritchard’s mission to scan the Cologne Cathedral stems both from preservation and modification. The Cologne Cathedral Administration, known natively as Metropolitankapitel der Hohen Domkirche Köln, commissioned the scanning project so that they can determine how to better conserve the structure – whether that be to produce replacement parts or produce future cathedrals with similar architectural design.
In the case of Pritchard’s motivation, he is working with CyArk to help ensure that his data is appropriately archived for future use, stating: “The world heritage precinct at Cologne is going to change over time, and a couple of 1950s buildings are going to come down. The scan data will be of tremendous value to do the planning and design.” Pritchard is also working in collaboration with a Cologne school, Hochschule Fresenius Köln, where they are working to create a way to help boost public engagement with the 3D scan data.