Photogrammetry in the Bell Tower
How many overlapping photographs became a usable digital record of the Propstglocke.
Photogrammetry means measuring shape from photographs. In this project, the bell could not be moved into a studio, so the capture had to work inside a narrow tower with changing light, wind, ladders, wooden beams, and strict time windows.
The images were not taken as one simple walk around the object. They were captured in layers: the outside of the bell, the inside and clapper, detailed reliefs and inscriptions, and the upper crown area. This helped the software understand both the large form and the small surface details.
What made the capture difficult
- The bell area had to be left roughly every 13 minutes, so some image sequences were interrupted.
- Lighting changed because room lights, sun, weather, and reflections on bronze all varied during the work.
- Wooden frame parts, other bells, windows, and moving objects could confuse feature matching if they were not masked.
- The upper and inner areas were hard to photograph safely, which increased blur and reduced useful viewing angles.
How the model was reconstructed
- Structure-from-Motion estimated camera positions and a first sparse point cloud from shared image features.
- Multi-View Stereo densified the reconstruction into depth maps, a dense point cloud, and finally a triangle mesh.
- Masks removed moving, blurred, or irrelevant background areas so the software focused on the bell.
- Difficult partial models were aligned manually when automatic matching was not reliable enough.