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232 Journal of the Spanish Institute for Strategic Studies Núm. 11 / 2018 For the application of these techniques several aerial images of the Calw city centre are used, which were supplied by the Landesamt für Geoinformation und Landentwicklung42. These images have geo-referenced coordinates of the projection centres and orientation angles, and have a Ground Sampling Distance (GSD) of 10 cm. The processing of these images in SURE comprises two steps. In the first, aerial images are corrected for distortion and rectified in pairs. In the second, suitable pairs of images are selected to which an algorithm similar to Semi-Global Matching (SGM) is applied. Finally, dense point clouds are generated with 10 cm spacing, which corresponds to a 3D point per pixel. The point cloud generated by aerial photogrammetry also serves as a reference for point clouds obtained with laser scanners. Data processing phase Once the information has been acquired with the different methods, a large volume of data represented in the form of point clouds is obtained spatially. This information is processed in two successive work steps: (a) the registration and (b) the 3D modelling/ texturing of the point clouds. Cyclone43 software was used for the process of registering the laser point clouds, as well as for CAD modelling in conjunction with Autodesk 3ds Max44. PhotoScan45 and SURE46 programmes were used to generate point clouds from images. Once the models had been obtained, Photoshop47 was used in the editing phase and the preparation of textures, which were then inserted into the CAD model using Sketchup48. Finally, the integration of the 3D models of buildings in a virtual environment was accomplished in Unity49. 42  LGL-BW, 2017. Website of Landesamt für Geoinformation und Landentwicklung de Baden- Württemberg: https://www.lgl-bw.de (Date accessed: 15 March, 2017). 43  Leica Geosystems AG, 2017. Leica Geosystems AG company website: http://leicageosystems.com (Date accessed: 15 March, 2017). 44  Autodesk Inc., 2017. Autodesk Inc company website: http://www.autodesk.com (Date accessed: 15 March, 2017). 45  Agisoft LLC, 2017. Agisoft LLC company website: http://www.agisoft.com (Date accessed: 15 March, 2017). 46  nFrames GmbH, 2017. nFrames GmbH company website: http://www.nframes.com (Date accessed: 15 March, 2017). 47  Adobe Systems Inc., 2017. Adobe Systems Incorporated company website: http://www.adobe.com (Date accessed: 15 March, 2017). 48  Trimble Inc., 2017. Trimble Inc. company website: http://www.trimble.com (Date accessed: 15 March, 2017). 49  Unity Techn., 2017. Unity Technologie company website: https://unity3d.com (Date accessed: 15 March, 2017). http://revista.ieee.es

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