# Graphic Applications of Unmanned Aerial Vehicles (UAVs) in the Study of Industrial Heritage Assets
## 1 Introduction
Furthermore, depending on the built-in image capture system, thermal and multispectral images can be generated. These functions are useful, among others, in efficiency energy studies or in the analysis of water resources, which can be applied in heritage research [23; 24]. Photogrammetry techniques are widely employed in different disciplines: architecture, topography, archaeology and cartography are some examples [25; 26; 27]. These techniques aim to calculate the dimensions and positions of objects in space, from measurements made with photographs. Photographs taken from the field can be employed, but the use of aerial photographs has allowed to carry out analysis of larger extensions of land, reducing the time required. In this sense, UAVs are considered a great interesting tool in the use of this techniques [28; 29; 30]. Besides, the aerial images facilitate the generation of 3D models, from photogrammetry techniques, which have a great interest in heritage research and assets' monitoring. [PERSON] et al., in [31], used an UAV on the Mozarabic church ruins in Bobastro (Malaga, Spain). The use of an UAV allowed them to take the necessary photographs of the ruins to generate a3D model using photogrammetry techniques. Additionally, a digital elevation model was produced in order to determine where the structure of the church was built. The final results were a virtual recreation of these archaeological ruins. A similar methodology was employed in [32], where the authors generated a 3D model of Hatfaludy Mansion, in Hida (Romania), using a UAV. The final research purpose was to generate enough information using the UAV to promote the asset as a local tourist attraction. Previously, this information can be integrable to heritage conservation and reconstruction process. [PERSON] et al. in [33] used a UAV to generate orthophoto maps for mapping and detecting cultural heritage sites in the coast of Lesvos Island (Greece). The UAV flight height was carried out at 100 m around Mytilene ancients harbour and the Eresos ancients harbour, with an orthophoto resolution of 2.5 cm/pixel, what shows the high capacity to capture images that an UAV has. Additionally, authors developed a metadata cataloguing system in order to facilitate online search operations. UAVs allow one to mount different camera typologies, depending on the type of images to be obtained. In [34], [PERSON] et al. employed a conventional photographic camera and a thermal Infrared camera to perform a thermal characterization of a dry-stone wall terraced vineyard in the Chianti area (Tuscany, Italy). [PERSON] installed an infrared camera in a UAV to produce a Normalized Difference Vegetation Index (NDVI) orthomosaics plan from different areas along a Roman road [35] in Avila (Spain). The purpose of these orthomosaic photos was to identify where the road crossed. In this sense, [PERSON] et al., in [36] used an UAV to take aerial photographs of the Anana Salt Valley and the Nueva Ceramica de Orio Factory, both of them in the Basque Country. Regarding the Salt Valley, UAV-assisted close-range photogrammetry enabled generation of a digital terrain model. On the other hand, for the Factory of Nueva Ceramica, the authors created a building information model (BIM). With this objective, outdoor and indoor photographs were captured using a UAV. The authors also analysed the difference between laser scanning and photogrammetry technique using a UAV. They observed that the UAV reduces capture time and economic cost. They also established that UAVs can be employed not only in larger land extensions, but also in more reduced areas in which laser scanners cannot be placed and used. Thus, the review of the scientific literature on the application of UAVs to cultural heritage assets allows one to identify interesting examples. Nevertheless, despite its potential, this technology has not yet been widely used in the study and management of industrial heritage, what opens a promising field of research.