# Review of Photogrammetric and Lidar Applications of UAV
## 6 Discussion
### Discussion on Applications of UAVs
#### 6.2.1 Mapping and Surveying
When choosing a suitable method, it is important to consider instrumentation, required accuracy, finances, point density, or the interpretation of the resulting outputs. However, the use of photogrammetric methods is more advantageous than the use of lidar technology due to the ease of data acquisition, its flexible and fast use, its low purchase price, and the high density of point clouds. The deployment of TLS and the SfM photogrammetric method has also been successful in the documentation of underground cave spaces [6; 74; 75] to create 3D models of them. The authors of [6] used the SfM photogrammetric method to take images with a Pentax K-5 DSLR digital camera with a Pentax SMC DA lens in Ochtina Aragonite Cave, Slovakia. The authors of [74] conducted a tectonic and morphological investigation of the Luo Shui Kong Cave. They used Agisoft PhotoScan(r) Professional Edition, version 1.2 software to process the images and point cloud, from which a 3D model was made. The UAV is also used in the mapping of surface karst areas. The authors of [76] investigated the area in the southwestern part of the geomorphological unit of the Slovak Karst using aerial and ground-based laser scanning. The airborne laser scanning data were obtained using a Leica ALS70-CM scanner. In total, 1.99 billion points with a point density of 29 points / m\({}^{2}\) were captured in the 68 km\({}^{2}\) area of interest. In reference [77], the authors evaluated and classified the vegetation of karst wetlands in Huixian Karst National Wetland Park, Guilin, South China, using a DJI Phantom 4 Pro UAV and an FC6310S camera. They collected data during 12 flights, which were processed using Pix4D Mapper software to generate orotophotomosaics and DSM. The publication [78] investigated the extraction of vegetation information in a karst area using a DJI Phantom 3E. They captured images with 4000 \(\times\) 3000 pixel resolution at a flight height of 150 m AGL. [PERSON] et al. [79] addressed biodiversity maintenance in karst areas. They chose the Maotiao Basin and Nanning Basin in the core of the South China Karst as their area of interest. Using DJI Phantom 4 Pro, they acquired 3507 images. Processing was performed using Pix4 Dmapper software to generate digital orthophotmaps with a spatial resolution ranging from 1.5 cm to 5.3 cm. The UAV imagery was used for tree and shrub identification and habitat classification. When documenting underground cave spaces and mapping surface karst areas, we recommend the SfM photogrammetric method. With its help, we can observe wetland vegetation, complex reliefs, and numerous karst caves in karst areas, as well as the extraction of vegetation with higher accuracy and better effect. The advantage of combining UAV and SfM is obtaining information about vegetation in complex terrain areas, saving research time, and obtaining more targeted plants. UAVs have also been applied in the mining industry [80; 81; 82; 83]. The review article [80] compiled 65 articles from 2010 to 2020. The articles used UAV AeroVironment RQ-11A Raven, Honeywell RQ-16A T-Hawk, Sensefly eBee, Skywalker X5, AscTec Falcon 8, DJI Phantom III, Aibotix Aibot X6v2, Albatros VT3, and Tholeg THO-R-PX8/10. As sensors,digital cameras, spectral imaging cameras, lidar, thermal infrared cameras, and gas sensors were mounted. Thanks to UAVs, the air was checked against hazardous substances from explosions in mines and quarries, mapped mineral extraction, or the exploration of the mined-out territory. The authors in the article [81] used a DJI S1000 UAV with camera Sony ILCE A7R to map the Piekary and Jaworzno area in 2016. In 2020, it was a BIRDIE UAV with a Sony DSC-RX1 RM2 camera. The deformations of the area caused by mining activity were surveyed. The results of spatial changes ranged from \(-0.5\) m to \(+0.4\) m. The article [82] dealt with the study and protection of sites affected by mining activities in northwestern Spain's Roman gold mining infrastructure. Non-contact technologies are used in such areas due to inaccessibility and remoteness.