# Review of Photogrammetric and Lidar Applications of UAV
## 6 Discussion
### Discussion on Applications of UAVs
#### 6.2.1 Mapping and Surveying
For the mapping, a DJI Phantom 4 with 12.4 Mpx FC330 camera was used. The flight was controlled using Pix4D field software. Based on the acquired data, seven models were created for the monitored site. All models were created from images from 270 to 536, except model nr. 7, which was generated using 63 images. Therefore, the GSD value of 13 cm is also less accurate for this model. For the others, the GSD ranged from 1.8 cm to 4.9 cm. The flight was performed at a height of 50 m AGL. The number of GCPs range from 4 to 9, and the RMSE was calculated. The worst GCP--RMSE was for model No. 7, whose value ranged from 8.8 cm to 41 cm. The best GCP--RMS was in model No. 5, which varied from 0.6 cm to 11 cm. Most of the models consisted of 3D texture, ortho-mosaic, and DEM. The UAV has been used to explore open pit mines in the articles [84; 85; 86]. The authors of the article [84] focused on the exploration of and research on iron mines in the Beijing area. Surface mining was observed in order to monitor changes and other processes in the area, such as pollution or erosion. The mapping of each open pit mine was carried out using the UAV SfM method. Furthermore, the purpose of this measurement was to mitigate the effects of anthropogenic changes caused by mining based on the geomorphological characteristics of the mines. The article [85] was devoted to a review of the UAVs used in the basin areas with their sensors in 2015-2018. The research used 40 articles published in Australia, China, Finland, and other countries. UAVs have been applied in various sectors such as 3D reconstruction and pollution monitoring. Different types of UAVs such as fixed-wing and multi-rotor devices were compared. Sensors such as digital cameras, thermal infrared cameras, and others were also reviewed. The article is also addressed the future development of UAVs, where improvements could be made in the form of data-processing speed, technical advancement, and others. The article [86] explored the application of a fast, inexpensive, and accurate method to monitor environmental changes affected by mining activities. A site in northeast Beijing was selected, where a UAV captured the area with two series of high-resolution images between 2014 and 2016. Using the SfM method, a DEM was created, from which geometric changes were assessed using DoD and SLLAC analyses. When monitoring soil surface deformations in areas affected by underground or surface mining, the application of UAV spatial data collection sensors has the advantage of performing quick field work and having a high detail of outputs while maintaining needed accuracy parameters. UAVs make it possible to document otherwise inaccessible parts of mines. The generation of high-resolution height models (DEM) from the results obtained using UAV is useful in the evaluation of geomorphic changes related to mining activities. The authors of the articles [87; 88; 89; 90; 91; 92; 93] discussed using UAVs in land registration. The article [87] highlights UAV photogrammetry and laser scanning for cadastral mapping purposes in the Czech Republic in 12 test areas. Many points (fence corners, building corners) surveyed by conventional geodetic methods (RTK-GNSS, total station) and by UAV technology were compared. UAV carriers Hexacopter G6, MAVinci SIRIUS, and Trimble UX5, where sensors such as Canon EOS 700D, LumixGX1, SONY ILCE-6000, and DMC-GX1 were used for mapping. According to the results, an accuracy of 14 cm was achieved in more than 80% of the measurements. When comparing laser scanning and photogrammetry, the accuracy of the points determined from the lidar-based point cloud was found to be approximately 18% higher than that of the point cloud obtained by the photogrammetric point cloud with the 2 cm GSD. The article also compares the costs of conventional geodetic measurement methods and the new UAV technology. The research addresses the necessary changes in organizational and technological processes for using UAV technology.