## 5 Conclusions  
The use of UAV platforms equipped with GNSS receivers that provide georeferencing without the use of GCPs is desirable when mapping large and dangerous areas, such as active rockfall areas, as there is no need to use GCPs, as with indirect georeferencing. In this study, we only tested the use of only the georeferencing of the bundle block adjustment (BBA) with PPK method, in comparison to the use of georeferencing of the BBA with GCPs, to see if it is possible to produce high-accuracy photogrammetric products in the case of rockfalls. The main motivation of the study was to improve the condition for field surveying of GCPs, which is labor-intensive, time-consuming, and, most importantly, dangerous. In the majority of cases, the accuracy of the X, Y and Z coordinates, in the case of the georeferencing of the BBA with the PPK method, did not exceed 0.050 m; in the case of orthomosaic, the accuracy of the X and Y coordinates did not exceed 0.034 m; and in case of DSM, the accuracy of the Z coordinate did not exceed 0.072 m. At one location, the results of georeferencing of the BBA with the PPK method were not comparable to those of georeferencing of the BBA with GCPs for all photogrammetric products, which was mostly due to the satellite configuration on the day of the UAV survey with the BBA_PPK method.  
We can conclude that the georeferencing of the BBA with the PPK method can provide high-accuracy products, presenting a viable alternative to the georeferencing of the BBA with GCPs. The decision regarding the use of the georeferencing method must be in line with the purpose of the final results; for example, in the regional modeling of rockfalls, at decimeter accuracy, the BBA georeferencing with the PPK method may be satisfactory, while the planning of technical protection measures with rockfalls, at centimeter accuracy, may require the use of GCPs. The PPK method presents a safer option for mapping in mountainous areas. To improve the accuracy of the BBA georeferencing with the PPKmethod (i.e., to centimeter accuracy), further analyses will be conducted, in combination with a smaller number of GCPs at certain locations in rockfall areas.  
Conceptualization, B.Z. and M.K.; methodology, B.Z. and M.K.; formal analysis, B.Z.; investigation, B.Z.; resources, M.K.; data curation, B.Z.; writing--original draft preparation, B.Z.; writing--review and editing, M.K.; visualization, B.Z.; supervision, M.K. Both authors have read and agreed to the published version of the manuscript.  
This research was supported by the Interreg Alpine Space projects \"ROCKtheALPS\" (ASP 462) and GreenRisk4 ALPs (ASP 635). The authors would like to express their gratitude to the Pahernik Foundation, for providing funds to publish this paper.  
Not applicable.  
The data presented in this study are available on request from corresponding author.  
The first author would like to additionally thank the Pahernik Foundation for co-financing the tuition for the doctoral study, of which this paper presents one of the major results. A special thanks also goes to the Triglav National Park, for issuing a permit for research work within the park.  
The authors declare no conflict of interest.