Image based 3D Reconstruction in Cultural Heritage Preservation

Documentation of the current state of an object is often the first crucial step in cultural heritage preservation. Especially for large scale objects as buildings this task becomes complex and time consuming. Hence, there is a growing interest in new, more efficient techniques, which ease the process and reduce the financial impact of surveying actions. In case of façade restoration, experts need to map damages and plan the corresponding measures, before the actual restoration can take place. Here, two-dimensional CAD drawings, depicting each single stone, serve as a basis. Traditionally these plans are derived from classical surveying. Often a photogrammetric approach is chosen to reduce the efforts on site. But still image processing, including image registration and point measurements, is carried out punctually and manually. Since about three years, our institute supports the introduction of modern image processing tool chains to the application field of heritage preservation. Recently we participated in the restoration of the tower facades of the St. Martin dome in Rottenburg/Neckar, Germany. We combined laser scans, terrestrial imagery and images captured from a UAV platform, incorporating structure-from-motion, dense image matching, point cloud registration and production of orthographic projections, from which the CAD drawings could be derived.