# Integrating a LiDAR Sensor in a UAV Platform to Obtain a Georeferenced Point Cloud
## 1 Introduction
Part of the development of the system was to consider the replacement of the LiDAR sensor by future models of smaller size and weight in the structure design. In addition, two types of software were developed to control the LiDAR-UAV system and processing of the LiDAR data. This low-cost system allowed obtaining the topographic and vegetation parameters necessary for biodiversity studies by obtaining high-density LiDAR data [19]. Among the fields that are adopting the use of LiDAR-UAV systems to improve their operations are agriculture [7; 20; 21], forestry sciences [19; 22], archaeology [23; 24], topography [8; 11; 19], bathymetry [25], building reconstruction [1; 26] and structural inspection [10; 27]. An UAV system equipped with a LiDAR scanner and a multi-spectral camera system was presented for the study of pre-Columbian Amazonian archaeology. The information collected by the LiDAR sensor has an 80% lateral overlap with six flight lines, three horizontal and three vertical. The result was the study of the structure of the forest and the reconstruction of surfaces under the forests for the identification of archaeological sites [23]. For identifying, mapping and interpreting mines from ancient Rome in northwestern Spain, integrated geometric applications based on information from a UAV system equipped with a LiDAR sensor have been reported. The 1 m resolution LiDAR sensor improved channel, water reservoir and mine resolution and survey capabilities. Furthermore, using a UAV system implemented with LiDAR systems for short and detailed surveys reduced the time of data collection and tool costs [24]. A fusion between a UAV system with a LiDAR sensor and spectral imaging was shown to identify plant species and 3D characterization at sub-meter scales. The resulting precision was between 84% and 89% for species classification, and the proposed system's digital elevation model (DEM) correlated with the DEM of a LiDAR-derived system, with an R2 of 0.98 and 0.96 [22]. Integrating LiDAR sensors and UAV platforms presented benefits in agriculture in observing the production and status of crops. A system was developed using a DJI Matrice100 UAV, an Odroid XU4, the Velodyne VLP-16 LiDAR sensor, a Point Gray Chamaleon3 3.2 MP Color camera, and a Sony imx265 sensor as part of the hardware and system. The ROS system was used to record the data. A variation in the height of the crops was found between 0.35 and 0.58 m. The components used and the mount design were made available online to be adapted to similar projects. The mount was printed in 3D nylon for this project and was designed considering the payload and the pinholes already included in the LiDAR sensor and inertial measurement unit (IMU) sensor [20]. The use of LiDAR-UAV systems in civil engineering can have many applications. For example, [PERSON] et al. (2020) proposed a flight planning method for the benefit of UAVs in bridge inspection, considering a Matrice 100 UAV and a Velodyne LiDAR PUCK for the test [27]. In [10], a platform for structural inspection was developed, integrating a UAV and a 2D LiDAR scanner. Similarly, [26] used a low-cost IMU and the Hokuyo UTM-30 LX sensor integrated this time into the UAV by an aluminum frame. Finally, [PERSON] et al. (2017) [1] proposed a LiDAR-UAV system to reconstruct urban environments, combining the UAV with an inertial navigation system (INS), a GNSS receiver, and a low-cost Velodyne VLP-16 LiDAR sensor. There has been increasing use of LiDAR sensors in various areas during the last years, mainly due to technological accessibility and diffusion worldwide. Other point cloud generation techniques, like photogrammetry, are limited because they depend on parameters associated with images like luminosity, meteorological conditions, and others [28]. The LiDAR sensor does not have this problem and can obtain information about places with difficult accessibility and restricted vision [29]. As a result, several companies have developed systems integrated with LiDAR for commercial use.