## 2 Materials and Methods
### Traditional Parameters for the Implementation of the Flight Project  
When setting the parameters of a photogrammetric flight developed with UAV aimed at the acquisition of information for the virtualization of objects/territories, the control of the UAV itself must be taken into account. This is due to the different flight alternatives that are available: automatic mode, monitored, supervised, preprogrammed, and remote controlled [7]. The automatic mode is the most applied option for the development of photogrammetric activities [8], as it guarantees a more homogeneous distribution of the images, while fulfilling the coverage requirements set [9]. This typology of flight is the most common when generating orthoimages or 3D models, and parameters such as the extent and morphology of the terrain, the photogrammetric camera, the scales of the photographs and the model, the flight height, the forward and lateral overlaps, the direction and track of the passes, the time of the flight, the day and hour, the coordinates of the points of the taking off and landing points, etc. must be considered for its programming. For the resolution of the flight project, the pilot establishes approximately three or four parameters, which estimates the global set of adjustments. In this regard, platforms manufacturers provide software that allows developing the required calculations nowadays, by setting exclusively four parameters (height of flight, forward and lateral overlap, and speed of flight), apart from the focal length of the photogrammetric camera that is used. All the foregoing implies that the pilot estimates the flight projects in a somewhat approximate way, without any methodology that allows optimizing these parameters, or suits the actual necessities of the modeled object or territory. To adapt the parameters applied for the dimensioning of the flight project, reviewing the ones that have been traditionally applied seems coherent. * The atmospheric constrains. These are a very important set of parameters that must be considered in any photogrammetric flight. They define the climatic and lighting conditions during the acquisition of the images. Despite their lack of influence on the geometry and the flight project itself, they must be identified in the first instance, as they can impede the development of the flight if they are severe, and even without being extreme, they may seriously affect the quality of the images and, therefore, the quality of the model [9]. * The sensor or photographic camera. They are not parameters themselves, but they usually constrain the flight. They are mainly defined by two technical features: the focal length and the size of the sensor. Two different types of cameras are applied in photogrammetry. When working in the range of low-cost sensors, which are also known as nonmetric cameras, their specifications are not fixed in a precise way by the manufacturer. This implies several sources or error that are usually soothed with methodology of surveying and management. It is worth noting that this research is focused on this type of sensors due to an obvious reason, i.e., the economic factor, which undoubtedly eases the current growth of this technique in the market. * The geometry or direction of the plane passes. They define the simple or double grid that can be applied for a photogrammetric flight. The simple grid, in which the flight has just one direction, easily adapts to models or mappings where the variability of the vertical component is scarce (plain terrains) [6]. The double grid (flight in two perpendicular directions) is suitable to model objects whose vertical component varies widely (upright structures, buildings, etc. ), in which hidden areas must be avoided while acquiring the photographs. * The photogrammetric support. It is not a parameter of the flight project itself, as it does not imply any interaction with the features set for the definition of how the platform must operate to acquire the images.