Page - 778 - in Book of Full Papers - Symposium Hydro Engineering

resolution of approximately 1.96″/px in horizontal and vertical direction, which corresponds to a spatial resolution of 1 mm at 100 m distance. Altogether, we acquired point clouds with around 10 million points and 300 OVC photos completely covering the Drossen dam. The fully automatic acquisition of scan and image data took about 4 hours in total. Fig. 4 displays the final 3D photo model of the Drossen dam. Fig. 4: Textured 3D photo model of the Drossen dam Apart from OVC images covering the complete dam, we captured OAC images of selective defects (dark ares of Fig. 4) and used them for texture mapping as well. Hence, large-scale textures and high-resolution textures are combined in one model providing a detailed documentation for areas of interest at relatively low memory capacity and computational cost. For defect regions, we generate ortho images with sequences of overlapping high-resolution OAC photos (see Fig. 5). While easy to handle, ortho images provide a valuable data basis for an objective assessment of the concrete’s state. It is now possible to measure on the dam’s surface without requiring direct access. Fig 5: Ortho image of a defect region on the downstream side of the Drossen dam (block 16), derived from 21 OAC textures (1 pixel corresponds to 2 mm on the surface) 778