# Graphic Applications of Unmanned Aerial Vehicles (UAVs) in the Study of Industrial Heritage Assets
## 1 Introduction  
Interest in historical and cultural heritage has evolved over time. Initially, it was related to the economic value associated to some movable and immovable assets. This value was the result of the materials employed, the materialization quality and the social meaning that owning these goods had, since these possessions were a sign of wealth and high social status [1]. Then early centuries of Middle Ages were a warlike period and a great number of assets were destroyed. In the Renaissance period, the heritage concept evolved considering that they are transmitters of knowledge, so they must be analysed and conserved [2]. In nineteenth century, the development of museums represented the initiation of cultural heritage democratization. This fact suggests that society, regardless of economic status, will be interested in historical and cultural heritage and it could be a knowledge transmission way for society [3]. Nowadays, the historical and cultural heritage idea encompasses all these facts taking into account that the historical and cultural heritage represent the identity of a society, being witnesses of a past that must be evoked and remembered. Therefore, heritage conservation, as well as the transmission of the knowledge generated from the study of heritage elements, must be of interest to current societies. In this sense, actually, numerous studies on cultural and historical assets are being carried out [4; 5; 6]. The following figure (Figure 1) graphically summarizes the described evolution of the heritage concept:  
During the last decades, industrial heritage has been internationally accepted as a heritage typology. The Water Management System of Augsburg (Germany) and the industrial city of the 20 th century in Ivrea (Italy) are examples of this typology included in the UNESCO World Heritage List [8]. Furthermore, different organizations and associations has been created recently to protect industrial heritage. In this sense, Association for Industrial Archaeology (AIA) or The International Committee for the Conservation of the Industrial Heritage (TICCIH) were created with this purpose [9; 10]. In comparison to other heritage typologies, industrial heritage has some special characteristics. Most of its assets date from the First Industrial Revolution, so it is a relatively young typology. Its relation to labour exploitation has provoked a certain initial social rejection. In spite of this, currently, this sense has been changing and the importance of this heritage typology is being recognized [11]. The loss of their original function and the pressure of urban development on many of their locations are other aspects that make the management and protection of these assets more difficult. Industrial heritage research should not be faced through approaches focused on particular industrial buildings or industrial equipment. The study of this typology should be considered as a whole [12]. Therefore, it is important to evaluate the industrial landscape which provides information about the moment of the activity develop [13]. Traditionally, graphic resources (photographs and videos) has been employed to document heritage assets. Furthermore, these graphic resources allow to generate high quality information to carry out interventions on heritage assets (conservation, restoration, etc.) or as a catalogue tool [14; 15; 16]. Nevertheless, this method does not always allow to obtain images of a complete asset. Elevated building areas (roofs) or difficult access areas are inappropriate environments to obtain good images in this  
Figure 1: Heritage concept evolution [7]. way [17; 18]. Thanks to recent technology evolution Unmanned Aerial Vehicles (UAVs) are able to solve these difficulties [19; 20; 21]. One of the advantages of the UAVs is that they can incorporate high-quality image capture systems generating high resolution photographs and high definition videos [22]. Thus, UAVs allow obtaining aerial images of large land areas and also accessing areas and spaces with difficult access at a lower cost.