## 3 Materials and Methods
### Methods
#### 3.1.4 Geological Applications of 3D Models
(**E**) Hyposmetric distribution of the deviation from the vertical (distance from the wall to the ration axis located at the base of the wall) in cm (color intervals each 10 cm) on the E side of the city wall; note the different sectors all constrained by the deformation caused by the earthquake. we decided to treat the elevation view of the walls of the buildings as maps with their own topography. In this case, we decided to apply this workflow to the North City-Wall Bastion of _Baelo Claudia_, specifically the east side of the city wall, which presents a remarkable level of preservation (Figures 3 and 5). This wall is N162E-oriented, shows strong deformation (both in the form of vertical axis folds and fractures) and nowadays is nearly vertical (Figure 3). For this work, once the appropriate photogrammetric reconstruction was performed in 3D (Figure 5A), we proceeded to isolate the data related only to the E wall of the architectural element. Once the photogrammetric reconstruction points of the 3D mesh were isolated, they were rotated 90 degrees clockwise from the base of the wall and with the axis parallel to the main direction of the wall (Figure 5B,C). This allowed the topographic reconstruction of this wall panel from almost vertical to almost horizontal (Figure 5C,D). This was done without distorting the overall dimensions of the reconstruction, just a rotation. The election of the main direction and the location of the rotation axis was relevant to illustrate the correct dimensions of the deformation suffered. In this case, we located the axis tangent at the most external part of the wall, core vertical deviation (green colors in Figure 5E). In seriously deformed structures, it can be difficult to locate a \"main direction\", and it is recommended to segment the study area into areas with similar characteristics to minimize subjectiveness. Subsequently, we obtained a DEM of the wall thus rotated 90 degrees and therefore now horizontal so that, by means of GIS computing, we could fully reach the potential of elevation data management that a GIS usually provides; see, for instance, a good-quality hillshade model in Figure 5D and a hyposometric distribution in Figure 5E. It is worth noting that, due to the rotation of the original topographic elevation points, the results of all GIS workflows and algorithms must be reinterpreted. For instance, a slope algorithm will offer the complementary angle of the actual slope due to the 90-degree rotation. This angle will identify the deviation from the vertical (90 degrees) suffered during the earthquake and, hence, the changes in dip from pre- to post-earthquake situation. Moreover, in a GIS environment, an aspect algorithm usually identifies the direction to which the downward slope points at each location for a DEM, and this slope characterizes the areas facing N, S E and W. However, after the rotation is applied to the elevation data of the studied wall, the aspect algorithm will now only identify left and right and vertical up and down. As the overall orientation of the wall is N162 E, the aspect domains can clearly be correlated as broadly NNW-SSE oriented, and the flanks and axis of existing vertical folds can be identified (this will be discussed later in the next sections). In the same manner, the hyposometric model of the rotated DEM of the wall (Figure 5E) indicates the separation (horizontal) in cm from a vertical plane with zero displacement from the ground, on the rotation axis. As we will see, all these models allow the precise identification and quantification of the deformation suffered in this wall, which would otherwise be quite difficult due to access and the overall low magnitude of the deformation in the fracturing, tilting and folding of this structure.