## 5 Experience in Building 3D Point Cloud and Orthophoto
### Beyond 3D Modelling  
UAV photogrammetry enables the construction of 3D models even in critical scenarios, such as the reconstruction of a masonry bridge from the late 1800s in a hard-to-reach area [128]. Once the 3D model has been built according to a mesh point cloud, it is possible to create models useful for heritage building information modelling (HBIM). For example, [PERSON] et al. [129], through a UAV photogrammetric approach and the implementation of a set of architectural building information, developed an HBIM model of the 'Averof Museum of Neo-Hellenic Art' located in Metsovo (Greece). [PERSON] et al. [130] discuss the construction of a BIM model of the Giorgini Bridge in Castiglione della Pescia, Grosseto (Italy), through the integration of UAV photogrammetry and terrestrial laser scanning. [PERSON] et al. [131] describe an accurate, simple, and cost-effective method to document CH sites and generate 3D digital models from images acquired by the UAV platform; the 3D model was managed in Autodesk Revit software environment to generate a BIM of the church taken into consideration.  
Other applications can be found in the transformation of the 3D model generated from UAV photogrammetry in the finite element model (FEM) or finite element analysis (FEA) model [132,133]. [PERSON] et al. [134] describe an experiment conducted at the Convent of San Francesco located in the centre of Monterubbiano (Marche, Italy). In particular, a 3D survey that integrated two different acquisition techniques was carried out: a TOF laser scanner and a 3D model based on images acquired by a UAV platform equipped with a digital camera. This approach was developed in order to obtain a dense 3D model from which high poly and low poly 3D models could be generated and which could be performant in the field of historical documentation and photorealistic representation, as well as valid support in the field of risk assessment based on the finite element method.  
[PERSON] et al. [135] describe an efficient method in order to obtain a FEM model of a bridge from a point cloud generated by UAV photogrammetry. In particular, the 3D point cloud was carried out using UAS Xiaomi Mi 4K, a multicopter rotary equipped with a 12 MP camera and Agisoft Metashape software. The point cloud was first imported into Rhinoceros software, and thanks to the implementation of some plug-ins developed in Grasshopper, the parametric model was built; subsequently, the model of the bridge was imported into Midas software to build a model suitable for FEM analysis (Figure 11).  
Figure 10: Several orthophotos of the spire generated from the 3D model.  
A widely used 2D approach from orthophotos concerns the construction of 2D CAD drawings that are particularly useful in the fields of archaeology and architecture [136]. An architectural application was realised for the construction of a CAD representation of the staircase of the church of San Domenico in Taranto (Italy), as shown in Figure 12.  
Figure 11: Masonry bridge from Roman times incorporated into a bridge from the 1800s and located in South of Italy: image of step acquisition (**a**) and FEM model of the arches of the bridge (**b**).  
Figure 12: _Cont._  
This photogrammetric survey was carried out with a Parrot Anafi drone in order to cover each element of the staircase and some structural elements that compose it where it is necessary to take zonal photos.  
The post-processing that led to the construction of an orthophoto with a pixel size of 5 mm was carried out with Metashape software; from this orthophoto, CAD restitution was carried out in such a way as to highlight the architectural elements that characterise the structure.