State Documentation of extensive underground Cavity System

Documentation of conservation state in large-scale subsurface objects. Scene reconstruction by structure-from-motion algorithms has received a great deal of attention due to the freely available software Bundler. We describe a workflow mainly based on Bundler, PMVS2 and Meshlab for a three-dimensional documentation of conservation state in subsurface objects. The presented procedure is also suitable for locations difficult to access. Specific challenges in subsurface objects need to be addressed. This contribution describes the employed photo recording and processing procedure. As a result, photo-realistic textured models are exported in WebGL format, which is viewable in recent web browsers. Experiments were performed in the abandoned ore mine "Thurm Rosenhof" in Clausthal-Zellerfeld, the karst cave "Bielshohle" in Rubeland and a drilling site of a potash mine. Two water wheel cambers and the connecting (and partly water-filled) adit of "Thurm Rosenhof' were photographically documented. 3D geometry and texture was reconstructed based on these images. The karst cave provides a second test object, which is characterized by a more irregular geometry and varying passage dimensions. The blast hole drilling site in potash mining provides an object where reference data from laser scanning is available, enabling comparisons to the data derived with the structure-from-motion based approach. Median point distance between both models was found to be 8 mm.