## 1 Introduction  
The goal of this paper is to study the performance of the digital aerial photogrammetry (UAV-DAP) in a multi-Rotor UAV with a 3D array of 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3D 3 3D 3  
## 1 Introduction  
UAV-based digital aerial photogrammetry (UAV-DAP) has become common worldwide due to its easy operation, time saved in data capture, low cost of data acquisition, and high spatial and temporal resolution compared to other photogrammetric techniques [1]. This technique uses SfM (Structure from Motion) algorithms that have been extensively tested and included in user-friendly programmes [2]. SfM is based on the sequential acquisition of 2D images to reconstruct 3D scene geometry [3]. When a point is visible in two or more images, correspondences are sought between the observations of this point in the different images. These represent the projection of the same 3D point in different images. Collinearity equations are solved by this technique without the addition of GCPs, considering that these equations can be solved in an arbitrary coordinate system. Therefore, flight conditions, overlapping images, different flight heights, or camera angles can modify processing and results [4]. UAV-DAP is used in various areas of geomatics, such as mapping or land surveying. This technique is more economical and straightforward in comparison with airborne laser scanning (ALS) [5] and superior to surveying methods in terms of data acquisition and time-saving in fieldwork [6; 7]. UAV-DAP can reach places that are difficult to access and terrains with a significant variation in slope, as the flight height can be changed to achieve greater spatial resolution [8; 9]. Another of the main advantages of using UAV-DAP is that by simply equipping it with a RGB (Red, Green, Blue) camera, it is possible to obtain photogrammetric products such as 3D point clouds, digital elevation models (DEMs), digital terrain models (DTMs) [10], orthomosaics, and 3D restitutions. In this sense, DTMs are one of the most essential resources for generating derived maps such as contours [11], hydrological analyses [12; 13; 14; 15; 16], visual basins [17], landslides [18; 19; 20], subsidence analysis [21; 22], and longitudinal profiles [23]. Also, with multispectral cameras, it is possible to classify species of trees and shrubs in forests [24; 25]. Due to the inherent relevance of UAV-DAP-derived products, obtaining high accuracy in some critical works is of great significance. UAVs can be classified as fixed-wing or multirotor, depending on their structure. Fixed-wing UAVs have more extended flight autonomy (over one hour with a single battery [26]) and require high flight altitudes and flight speeds due to aerodynamics, and usually, lower spatial resolution deliverables are obtained and can cover a greater area, but this equipment is costly, and some problems might arise in case of emergency situations. Multirotor UAVs usually yield higher spatial resolution due to lower altitude and slower speed, can be easily operated in narrow areas, and are less expensive, but at the cost of reduced flight time, as most of these devices have a battery duration of 15 to 30 min [27]. This is a limiting factor for covering large areas, and optimal flight planning is required to cover these areas with the lowest possible battery consumption without compromising the photogrammetric outputs' resolution. Several aspects must be considered when planning flights, influencing the accuracy of the products obtained from UAV measurement:  
* Flight planning parameters, including: (1) flight height: this determines the spatial resolution of the registered images and the number of images per unit area [28]; the greater the height, the lower the spatial resolution, but the larger the area that can be covered.