# Graphic Applications of Unmanned Aerial Vehicles (UAVs) in the Study of Industrial Heritage Assets
## 2 SWOT Analysis Applied to UAV
### Opportunities  
Regarding the opportunities, different aspects that represent the potential applications of UAVs in heritage research have been considered:  
O1. Aerial Image Performance: Currently, aerial image generation with UAVs is the most widely used application. Conventional photo or video capture systems require a physical support to capture zones that cannot be observed on land. This is usually expensive and can cause user risks. Notwithstanding, UAVs image capture systems allow obtaining images in any area without the need for any external support and without user risk (S4). Furthermore, the image capture quality is on the order with that achieved with conventional capture systems. Another aerial image performance advantage with UAVs is the possibility to make orthophotographs, that can be applied to obtain indirect measurements between captured elements. In heritage asset analysis, the aerial images can be employed to analyse the environment in which the assets are located, generating a greater context for the study. In addition, aerial images in heritage assets promotional videos can increase interest in visiting it. O2. Image capture device combinations: Most UAV models allow the incorporation of different image capture devices that can generate photographs in the visible or infrared spectrum, thermographic or multispectral. Some of them allow one to do so from different positions and take different images on a single flight. However, others require the plane to land to change out the imaging device. The application of infrared and thermographic images can be considered in the conservation and restoration of heritage assets, being widely used in the energy efficiency analysis [48; 49]. On the other hand, multispectral images can be employed to analyse the environment in which the heritage assets are located. O3. Low inspection cost in hard-to-reach areas: Sometimes, access to certain areas is prevented, due to the state of conservation of heritage assets. For the O1 opportunity, the use of UAVs reduces the cost of external supports (scaffolding or lifting equipment) needed to enable inspection. O4. Extensive areas analysis. The UAVs flight allows observing the assets from a different perspective. Aerial images can show the environment where the asset is situated. Furthermore, the distribution of the different buildings that were part of the assets can be observed. This fact enriches the information about how the industrial activity was carried out. Opposite, conventional photography on the ground only allows generating individual images for the asset elements, losing the context where they are placed. O5. Asset digitalization models. The actual technology development allows one to generate 3D models, applying photogrammetric techniques. The UAV can capture different orthophotographs from a land area for inspection operation and then a terrain topographic survey can be generated. Furthermore, a photograph set, representing different positions of an asset, can be used to generate a 3D model of it. Actually, building information models (BIMs) have become a tool of great interest in building situations. In this sense, the UAV use allows one to generate a 3D model that can be used as a starting point for a BIM generation. In addition, in the heritage field, this information model can be applied in conservation projects, where graphic information is required prior to the conservation activities, considering a heritage building information model (HBIM) [50; 51]. O6. Indirect measurements. A photograph can be considered as an object scale representation. From a real measurement reference that appear in the image, the remaining dimensions of the represented object can be obtained using indirect measurements. This method can be applied to measure elements that present a difficult access, complex geometry or large dimensions to measure using direct measurement methods.