# Graphic Applications of Unmanned Aerial Vehicles (UAVs) in the Study of Industrial Heritage Assets
## Case Study and Results
### Conventional and UAV Photography Comparison  
The use of UAVs has shown different opportunities for application to industrial heritage studies. In spite of this, conventional photography is still widely employed in heritage analysis. In this section, a comparison between UAV application and conventional photography has been carried out. Different characteristics have been considered to compare them:  
Figure 9: Comparison between conventional and UAV application photograph. The different variables are: CC: Conventional camera position; _UAV_: UAV position; _h:_ UAV flight height; \(l_{UAV}\): Distance from the UAV to the element to be measured; \(l_{cc}\): Distance from the conventional camera to the element to be measured; \(\theta_{cc}\): Conventional camera angle observation with the element to be measured; \(W_{R}\): Reference dimension. C1. Low equipment cost. Conventional camera technology is widely developed and nowadays, the acquisition costs of a conventional camera producing good quality images is low, around $90. On the other hand, a UAV with similar image acquisition potential costs $400. It is important to stand highlight out that the UAV system increases the cost due to the flight technology required. C2. Image perspective possibilities. Conventional cameras only allow taking pictures on the ground. This fact prevents from one from obtaining images of elevated areas in heritage assets such as the status of the building roof, requiring external elements to achieve it. Nevertheless, the UAV can generate images from different perspectives, being the aerial perspective a resource to photograph areas that cannot be observed on the ground, and it requires shorter times in comparison with conventional photography. C3. Accessibility. Occasionally, heritage asset structures are in a dilapidated state, so the access to its interior can be complex or can pose a risk to the user. In this sense, the use of UAVs enables one to access these complex areas without personal risk. On the other hand, UAV flight operation requires high pilot skill if the space is reduced. C4. Indirect measurement. One usual action in heritage assets evaluation is to measure singular elements or the surface extension where the assets are located. Furthermore, the measurement of deteriorated elements allows to one to decide if conservation actions need to be carried out. Direct measurement of elements located in complex access zones or elements with high dimensionality require non-conventional measurement equipment, which is expensive. Indirect measurements using photographs and reference measurements can be considered a solution. However, simple photographs generate cosine errors in the indirect measurement. In spite of this, a set of images in different positions allows one to generate orthophotographs that represent a scale of the element in its true magnitude. In this case, the use of UAVs can generate images from different positions and allows one to obtain indirect measurements with high accuracy. In addition, zenith photographs of elements located at a ground level are more easily obtained from aerial images. C5. Large area images. Heritage assets cannot be considered as an isolated element. The environment where the asset is located or the relationship between the different elements that the asset constitutes, provides information for the heritage analysis. Aerial images offer the possibility of to evaluating the assets completely. Furthermore, elevated points to take pictures allow one to represent the environment around the assets and observe or interpret the relationship it may have had with this environment. Conventional images taken on the ground, reduce the image extension or the presence of different obstacles can prevent it. C6. Usability. Technology application require specific knowledge by the user. The use of conventional photographic equipment is a fairly widespread technology which does not require a deep learning to generate the images.