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Eventually, we use 3D Delaunay triangulation to compute a triangle mesh, i.e. a set of triangles connecting the denoised point cloud. Dependent on the properties of the captured images, we apply automated image processing techniques to reduce radiometric differences and thus to obtain a homogenous texture. Due to the knowledge about the orientation of each image, the textures are mapped onto the surface model, which is why this step is called texture mapping. As a result, a photorealistic representation of the dam’s surface is obtained, which we then map onto a 2D plane to derive an ortho image with metric information. 2.3. FIELD STUDY AT AN AUSTRIAN ARCH DAM To validate our approach, we performed practical measurements at the Drossen dam, which is located near Kaprun, Salzburg. It is 112 m high, has a crest length of about 360 m, and is thus one of the largest dams in Austria. Together with the Mooser dam, it impounds the Mooserboden reservoir. Due to the large object-to-instrument distances (up to 200 m) and the scan range limitations, at least two setup points were required to cover the full dam. In order to speed up the data acquisition, we decided to use two total stations simultaneously set up at P1 and P2 (see Fig. 3 left). We used fixed points with known coordinates to reference measurements from both instruments in the national reference system. We decided to use a Leica Multi Station MS50 and MS60. Both instruments use the same hardware for scanning and imaging. The instrument scans up to 1000 points per second with an accuracy of 2 mm at 100 m distance. Fig 3: Measurement site, overview image showing the two concrete dams of the reservoir Mooserboden (left, source: Verbund), illustration of the relevant components of the Multi Station MS60 (right) The used instruments offer two cameras: the Overview Camera (OVC) and the On-Axis Camera (OAC). The OVC is a wide-angle camera with fixed focus and a large field of view (FOV) located above the telescope (see Fig. 3 right), whereas the OAC has a small FOV but benefits from the telescope’s 30× magnification, providing image content rich in detail. Calibration of the OAC [7] gives an angular Drossen dam Mooser dam 𝑷 𝟏 𝑷 𝟐 777