{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,27]],"date-time":"2026-03-27T17:10:40Z","timestamp":1774631440587,"version":"3.50.1"},"reference-count":70,"publisher":"MDPI AG","issue":"19","license":[{"start":{"date-parts":[[2021,9,23]],"date-time":"2021-09-23T00:00:00Z","timestamp":1632355200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"Interreg Alpine Space project &quot;ROCKtheALPS&quot;","award":["ASP 462"],"award-info":[{"award-number":["ASP 462"]}]},{"name":"Interreg Alpine Space project &quot;GreenRisk4ALPs&quot;","award":["ASP 635"],"award-info":[{"award-number":["ASP 635"]}]},{"name":"Pahernik foundation","award":["Pahernik foundation"],"award-info":[{"award-number":["Pahernik foundation"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Unmanned aerial photogrammetric surveys are increasingly being used for mapping and studying natural hazards, such as rockfalls. Surveys using unmanned aerial vehicles (UAVs) can be performed in remote, hardly accessible, and dangerous areas, while the photogrammetric-derived products, with high spatial and temporal accuracy, can provide us with detailed information about phenomena under consideration. However, as photogrammetry commonly uses indirect georeferencing through bundle block adjustment (BBA) with ground control points (GCPs), data acquisition in the field is not only time-consuming and labor-intensive, but also extremely dangerous. Therefore, the main goal of this study was to investigate how accurate photogrammetric products can be produced by using BBA without GCPs and auxiliary data, namely using the coordinates X0, Y0 and Z0 of the camera perspective centers computed with PPK (Post-Processing Kinematic). To this end, orthomosaics and digital surface models (DSMs) were produced for three rockfall sites by using images acquired with a DJI Phantom 4 RTK and the two different BBA methods mentioned above (hereafter referred to as BBA_traditional and BBA_PPK). The accuracy of the products, in terms of the Root Mean Square Error (RMSE), was computed by using verification points (VPs). The accuracy of both BBA methods was also assessed. To test the differences between the georeferencing methods, two statistical test were used, namely a paired Student\u2019s t-test, and a non-parametric Wilcoxon signed-rank. The results show that the accuracy of the BBA_PPK is inferior to that of BBA_traditional, with the total RMSE values for the three sites being 0.056, 0.066, and 0.305 m, respectively, compared to 0.019, 0.036 and 0.014 m obtained with BBA_traditional. The accuracies of the BBA methods are reflected in the accuracy of the orthomosaics, whose values for the BBA_PPK are 0.039, 0.043 and 0.157 m, respectively, against 0.029, 0.036 and 0.020 m obtained with the BBA_traditional. Concerning the DSM, those produced with the BBA_PPK method present accuracy values of 0.065, 0.072 and 0.261 m, respectively, against 0.038, 0.060 and 0.030 m obtained with the BBA_traditional. Even though that there are statistically significant differences between the georeferencing methods, one can state that the BBA_PPK presents a viable solution to map dangerous and exposed areas, such as rockfall transit and deposit areas, especially for applications at a regional level.<\/jats:p>","DOI":"10.3390\/rs13193812","type":"journal-article","created":{"date-parts":[[2021,9,27]],"date-time":"2021-09-27T22:16:38Z","timestamp":1632780998000},"page":"3812","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":28,"title":["Accuracy Assessment of UAV-Photogrammetric-Derived Products Using PPK and GCPs in Challenging Terrains: In Search of Optimized Rockfall Mapping"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-3167-8880","authenticated-orcid":false,"given":"Barbara","family":"\u017dabota","sequence":"first","affiliation":[{"name":"Department of Forestry and Forest Renewable Resources, Biotechnical Faculty, University of Ljubljana, Ve\u010dna pot 83, 1000 Ljubljana, Slovenia"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8013-6164","authenticated-orcid":false,"given":"Milan","family":"Kobal","sequence":"additional","affiliation":[{"name":"Department of Forestry and Forest Renewable Resources, Biotechnical Faculty, University of Ljubljana, Ve\u010dna pot 83, 1000 Ljubljana, Slovenia"}]}],"member":"1968","published-online":{"date-parts":[[2021,9,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"163","DOI":"10.5194\/nhess-15-163-2015","article-title":"Brief communication: The use of unmanned aerial vehicle in a rockfall emergency scenario","volume":"15","author":"Giordian","year":"2015","journal-title":"Nat. Hazards Earth Syst. Sci."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"321","DOI":"10.5194\/nhess-18-321-2018","article-title":"UAV-based mapping, back analysis and trajectory modeling of a coseismic rockfall in Lefkada island, Greece","volume":"18","author":"Saroglou","year":"2018","journal-title":"Nat. Hazards Earth Syst. Sci."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Sarro, R., Riquelme, A., Garcia-Davalillo, J.C., Mateos, R.M., Tom\u00e1s, R., Pasto, J.L., Cano, M., and Herrera, G. (2018). Rockfall simulation based on UAV photogrammetry data obtained during and emergency declaration: Application at a cultural heritage site. Remote Sens., 10.","DOI":"10.3390\/rs10121923"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"2027","DOI":"10.1007\/s10346-020-01416-4","article-title":"UAVs for monitoring, investigation, and mitigation design of a rock slope with multiple failure mechanisms\u2014a case study","volume":"17","author":"Rodriguez","year":"2020","journal-title":"Landslides"},{"key":"ref_5","first-page":"82","article-title":"Use of unmanned aerial vehicles (UAVs) for photogrammetric surveys in rockfall instability studies","volume":"24","author":"Danzi","year":"2013","journal-title":"Rend. Online Soc. Geol. Ital."},{"key":"ref_6","first-page":"EGU2015","article-title":"UAV-based natural hazard management in high-alpine terrain\u2014Case studies from Austria","volume":"17","author":"Sotier","year":"2015","journal-title":"Geophys. Res. Abstr."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"287","DOI":"10.5194\/nhess-18-287-2018","article-title":"Use of a remotely piloted aircraft system for hazard assessment in a rocky mining area (Lucca, Italy)","volume":"18","author":"Salvini","year":"2018","journal-title":"Nat. Hazards Earth Syst. Sci."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Vanneschi, C., Di Camillo, M., Aiello, E., Bonciani, F., and Salvini, R. (2019). SfM-MVS photogrammetry for rockfall analysis and hazard assessment along the ancient roman via flamina road at the Furlo Gorge. ISPRS Int. J. Geoinf., 8.","DOI":"10.3390\/ijgi8080325"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"79","DOI":"10.1016\/j.isprsjprs.2014.02.013","article-title":"Unmanned aerial systems for photogrammetry and remote sensing: A review","volume":"92","author":"Colomina","year":"2014","journal-title":"ISPRS J. Photogramm."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/s12518-013-0120-x","article-title":"UAV for 3D mapping applications: A review","volume":"6","author":"Nex","year":"2014","journal-title":"Appl. Geomat."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1080\/19475705.2017.1315619","article-title":"Use of unmanned aerial vehicles in monitoring and application and management of natural hazards","volume":"8","author":"Giordian","year":"2017","journal-title":"Geomat. Nat. Haz. Risk"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Buill, F., N\u00fa\u00f1ez-Andr\u00e9s, M.A., Lantada, N., and Prades, A. (2016, January 5\u20139). Comparing of Photogrammetric Techniques for rockfalls monitoring. Proceedings of the Word Multidisciplinary Earth Sciences Symposium (WMESS 2016), Prague, Czech Republic.","DOI":"10.1088\/1755-1315\/44\/4\/042023"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"23","DOI":"10.1186\/s40677-016-0060-y","article-title":"UAV-based photogrammetry and geocomputing for hazards and disaster risk monitoring\u2014A review","volume":"3","author":"Gomez","year":"2016","journal-title":"Geoenviron. Disasters"},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"110","DOI":"10.1016\/j.geomorph.2012.12.020","article-title":"Photogrammetry and laser scanning for analyzing slope stability and rock fall runout along the Domodossola-Iselle railway, the Italian Alps","volume":"185","author":"Salvini","year":"2013","journal-title":"Geomorphology"},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1931","DOI":"10.1007\/s11069-015-1811-x","article-title":"Calibration of restitution coefficients using rockfall simulations based on 3D photogrammetry model: A case study","volume":"78","author":"Kim","year":"2015","journal-title":"Nat. Hazards"},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"129","DOI":"10.1139\/cgj-2014-0051","article-title":"Comparison of airborne laser scanning, terrestrial laser scanning, and terrestrial photogrammetry for mapping differential slope change in mountainous terrain","volume":"52","author":"Lato","year":"2015","journal-title":"Can. Geotech. J."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Manousakis, J., Zekkos, D., Saroglou, H., and Clark, M. (2016, January 20\u201321). Comparison of UAV-enabled photogrammetry-based 3D point clouds and interpolated DSMs of sloping terrain for rockfall hazard analysis. Proceedings of the International Archives of the Photo-grammetry, Remote Sensing and Spatial Information Sciences, 11th 3D Geoinfo Conference, Athens, Greece.","DOI":"10.5194\/isprs-archives-XLII-2-W2-71-2016"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"909","DOI":"10.5194\/isprs-archives-XLI-B5-909-2016","article-title":"The potential of low-cost RPAS multi-view re-construction of sub-vertical rock faces","volume":"XLI-B5","author":"Thoeni","year":"2016","journal-title":"Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"6539","DOI":"10.1007\/s10064-021-02306-2","article-title":"Identification of potential rockfall sources using UAV-derived point cloud","volume":"80","author":"Albarelli","year":"2021","journal-title":"Bull. Eng. Geol. Environ."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"325","DOI":"10.5194\/nhess-19-325-2019","article-title":"Brief communication: Remotely piloted aircraft systems for rapid emergency response: Road exposure to rockfall in Villanova di Accumoli","volume":"19","author":"Santangelo","year":"2019","journal-title":"Nat. Hazards Earth Syst. Sci."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"260","DOI":"10.1007\/s12665-019-8145-z","article-title":"Multistep slope stability analysis based on unmanned aerial vehicle photogrammetry","volume":"78","author":"Wang","year":"2019","journal-title":"Environ. Earth Sci."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"107036","DOI":"10.1016\/j.geomorph.2020.107306","article-title":"Post-seismic monitoring of cliff mass wasting using an unmanned aerial vehicle and field data at Egremni, Lefkada Island, Greece","volume":"367","author":"Koukouvelas","year":"2020","journal-title":"Geomorphology"},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Macciotta, R., Gr\u00e4pel, C., and Skirrow, R. (2020). Fragmented rockfall volume distribution from photogrammetry-based structural mapping and discrete fracture networks. Appl. Sci., 10.","DOI":"10.3390\/app10196977"},{"key":"ref_24","first-page":"380","article-title":"The use of direct georeferencing in aerial photogrammetry with micro UAV","volume":"48","author":"Gabrlik","year":"2015","journal-title":"IFAC-Pap."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"220","DOI":"10.1016\/j.nrjag.2018.05.003","article-title":"Using RTK and VRS in direct geo-referencing of the UAV imagery","volume":"7","author":"Rabah","year":"2018","journal-title":"NRIAG J. Astron. Geophys."},{"key":"ref_26","unstructured":"Cramer, M., Stallmann, D., and Haala, N. (2020, January 16\u201323). Direct geo-referencing using GPS\/inertial exterior orientations for photogrammetric applications. Proceedings of the International Archives of Photogrammetry and Remote Sensing, Amsterdam, The Netherlands."},{"key":"ref_27","doi-asserted-by":"crossref","unstructured":"Forlani, G., Diotri, F., di Cella, U.M., and Roncella, R. (2019). Indirect UAV strip georeferencing by on-board GNSS data under poor satellite coverage. Remote Sens., 11.","DOI":"10.3390\/rs11151765"},{"key":"ref_28","doi-asserted-by":"crossref","unstructured":"Toma\u0161t\u00edk, J., Mokro\u0161, M., Surov\u00fd, P., Grzn\u00e1rov\u00e1, A., and Mergani\u010d, J. (2019). UAV RTK\/PPK method\u2014An optimal solution for mapping inaccessible forested areas?. Remote Sens., 11.","DOI":"10.3390\/rs11060721"},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"24","DOI":"10.1016\/j.isprsjprs.2020.05.015","article-title":"Mapping quality prediction for RTK\/PPK-equipped micro-drones operating in complex natural environment","volume":"167","author":"Cledat","year":"2020","journal-title":"ISPRS J. Photogramm."},{"key":"ref_30","doi-asserted-by":"crossref","unstructured":"Sanz-Ablanedo, E., Chandle, J.H., Rodr\u00edguez-P\u00e9rez, J., and Ord\u00f3\u00f1ez, C. (2018). Accuracy of unmanned aerial vehicle (UAV) and SfM photogrammetry survey as a function of the number and location of ground control points used. Remote Sens., 10.","DOI":"10.3390\/rs10101606"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"507","DOI":"10.5194\/isprs-archives-XLIII-B1-2020-507-2020","article-title":"Are measured ground control points still required in UAV based large scale mapping? Assessing the positional accuracy of an RTK multi-roto platform","volume":"XLIII-B1-2020","author":"Chiabrando","year":"2020","journal-title":"Int. Arch. Photogramm. Remote. Sens. Spat. Inf. Sci."},{"key":"ref_32","doi-asserted-by":"crossref","unstructured":"Benassi, F., Dall\u2019Asta, E., Diotri, F., Forlani, G., Morra di Cella, U., Roncella, R., and Santise, M. (2017). Testing accuracy and repeatability of UAV blocks oriented with GNSS-supported aerial triangulation. Remote Sens., 9.","DOI":"10.3390\/rs9020172"},{"key":"ref_33","first-page":"67","article-title":"The test field for UAV accuracy assessments","volume":"XLI-1\/W2","author":"Pyka","year":"2019","journal-title":"Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci."},{"key":"ref_34","unstructured":"(2021, April 18). DJI Phantom 4 RTK. Available online: https:\/\/www.dji.com\/si\/phantom-4-rtk."},{"key":"ref_35","unstructured":"(2021, May 11). senseFly 2021. Available online: https:\/\/www.sensefly.com\/."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"21","DOI":"10.5623\/cig2016-102","article-title":"Spatial accuracy of UAV-derived orthoimagery and topography: Comparing photogrammetric models processed with direct geo-referencing and ground control points","volume":"70","author":"Hugenholtz","year":"2016","journal-title":"Geomatica"},{"key":"ref_37","first-page":"130","article-title":"Comparison of four UAV georeferencing methods for environmental monitoring purposes focusing on the combined use with airborne and satellite remote sensing platforms","volume":"75","author":"Planas","year":"2019","journal-title":"Int. J. Appl. Earth Obs. Geoinf."},{"key":"ref_38","doi-asserted-by":"crossref","unstructured":"Mian, O., Luter, J., Lipa, G., Hutton, J.J., Gavelle, E., and Borghini, S. (2015). Direct georeferencing on small unmanned aerial platforms for improved reliability and accuracy of mapping without the need for ground control points. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-1\/W4, Proceedings of the International Conference on Unmanned Aerial Vehicles in Geomatics, Toronto, Canada, 30 August\u20132 September 2015, ISPRS.","DOI":"10.5194\/isprsarchives-XL-1-W4-397-2015"},{"key":"ref_39","doi-asserted-by":"crossref","unstructured":"Fazeli, H., Samadzadegan, F., and Dadrasjavan, F. (2016, January 12\u201319). Evaluating the potential of RTK-UAV for automatic point cloud generation in 3D rapid mapping. Proceedings of the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLI-B6, XXIII Congress, Prague, Czech Republic.","DOI":"10.5194\/isprsarchives-XLI-B6-221-2016"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"807","DOI":"10.5194\/esurf-7-807-2019","article-title":"Evaluating the potential of post-processing kinematic (PPK) georeferencing for UAV-based structure-from-motion (SfM) photogrammetry and surface change detection","volume":"7","author":"Zhang","year":"2019","journal-title":"Earth Surf. Dynam."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"165","DOI":"10.1080\/10095020.2019.1710437","article-title":"Accuracy assessment of real-time kinematics (RTK) measurements in unmanned aerial vehicles (UAV) for direct geo-referencing","volume":"23","author":"Ekaso","year":"2020","journal-title":"Geo Spat. Inf. Sci."},{"key":"ref_42","doi-asserted-by":"crossref","unstructured":"Mian, O., Luter, J., Lipa, G., Hutton, J.J., Gavelle, E., and Borghini, S. (2016). Accuracy assessment of direct georeferencing for photogrammetric applications on small unmanned aerial platforms. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-3\/W4, Proceedings of the EuroCOW 2016, the European Calibration and Orientation Workshop, Lausanne, Switzerland, 10\u201312 February 2016, Applanix.","DOI":"10.5194\/isprs-archives-XL-3-W4-77-2016"},{"key":"ref_43","doi-asserted-by":"crossref","unstructured":"Forlani, G., Dall\u2019Asta, E., Diotri, F., Morra di Cella, U., Roncella, R., and Santise, M. (2018). Quality assessment of DSMs produced from UAV flights georeferenced with on-board RTK positioning. Remote Sens., 10.","DOI":"10.3390\/rs10020311"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"9","DOI":"10.5194\/isprs-archives-XLIII-B2-2020-9-2020","article-title":"UAV block georeferencing and control by on-board GNSS data","volume":"XLIII-B2-2020","author":"Forlani","year":"2020","journal-title":"Int. Arch. Photogramm. Remote Sens. Spatial Inf. Sci."},{"key":"ref_45","doi-asserted-by":"crossref","unstructured":"\u0160troner, M., Urban, R., Reindl, R., Seidl, J., and Brou\u010dek, J. (2020). Evaluation of the georeferencing accuracy of a photogrammetric model using a quadrocopter with onboard GNSS RTK. Sensors, 20.","DOI":"10.3390\/s20082318"},{"key":"ref_46","doi-asserted-by":"crossref","unstructured":"Taddia, Y., Gonz\u00e1lez-Garc\u00eda, L., Zambello, E., and Pellegrinelli, A. (2020). Quality assessment of photogrammetric models for fa\u00e7ade and building reconstruction using DJI Phantom 4 RTK. Remote Sens., 12.","DOI":"10.3390\/rs12193144"},{"key":"ref_47","doi-asserted-by":"crossref","unstructured":"\u0160troner, M., Urban, R., Seidl, J., Reindl, T., and Brou\u010dek, J. (2021). Photogrammetry using UAV-mounted GNSS RTK georeferencing strategies without GCPs. Remote Sens., 13.","DOI":"10.3390\/rs13071336"},{"key":"#cr-split#-ref_48.1","doi-asserted-by":"crossref","unstructured":"Tufarolo, E., Vanneschi, C., Casella, M., and Salvini, R. (2019). Evaluation of camera positions and ground control points quality in a GNSS-RTK based UAV survey: Preliminary results from a practical test in morphological very complex areas. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-2\/W13","DOI":"10.5194\/isprs-archives-XLII-2-W13-637-2019"},{"key":"#cr-split#-ref_48.2","unstructured":"Proceedings of the Geospatial Week 2019, Enschede, The Netherlands, 10-14 June 2019, ISPRS."},{"key":"ref_49","doi-asserted-by":"crossref","unstructured":"Teppati Los\u00e8, L., Chiabrando, F., and Tonolo, F.G. (2020). Boosting the timeliness of UAV large scale mapping. Direct georeferencing approaches: Operational strategies and best practices. ISPRS Int. J. Geo.-Inf., 9.","DOI":"10.3390\/ijgi9100578"},{"key":"ref_50","doi-asserted-by":"crossref","unstructured":"Taddia, Y., Stecchi, F., and Pellegrini, A. (2020). Coastal mapping using DJI Phantom 4 RTK in post-processing kinematic mode. Drones, 4.","DOI":"10.3390\/drones4020009"},{"key":"ref_51","doi-asserted-by":"crossref","unstructured":"Caroti, G., Zaragoza, M.-E., and Piemonte, A. (2015). Accuracy assessment in structure from motion 3D reconstruction from UAV-born images The influence of the data processing methods. International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XL-1\/W4, Proceedings of the International Conference on Unmanned Aerial Vehicles in Geomatics, Toronto, Canada, 30 August\u20132 September 2015, ISPRS.","DOI":"10.5194\/isprsarchives-XL-1-W4-103-2015"},{"key":"ref_52","unstructured":"Jurkov\u0161ek, B. (1987). Tolma\u010d Listov Beljak in Ponteba: Osnovna Geolo\u0161ka Karta, SFRJ 1:100,000, Zvezni Geolo\u0161ki Zavod."},{"key":"ref_53","doi-asserted-by":"crossref","first-page":"205","DOI":"10.5474\/geologija.2008.021","article-title":"Osnovne tektonske raz\u010dlenitve Slovenije","volume":"51","author":"Placer","year":"2008","journal-title":"Geologija"},{"key":"ref_54","first-page":"285","article-title":"Pelagic Jurassic and Cretaceous beds in the western part of the Julian Alps","volume":"31","author":"Ogorelec","year":"2020","journal-title":"Geologija"},{"key":"ref_55","unstructured":"(2021, April 19). ArcGIS Pro 2.7.3, Esri. Available online: https:\/\/www.esri.com\/en-us\/arcgis\/products\/arcgis-pro\/resources."},{"key":"ref_56","doi-asserted-by":"crossref","first-page":"4","DOI":"10.1016\/j.geomorph.2015.05.011","article-title":"Reproducibility of UAV-based earth topography reconstructions based on Structure-from-Motion algorithms","volume":"260","author":"Clapuyt","year":"2016","journal-title":"Geomorphology"},{"key":"ref_57","first-page":"221","article-title":"Assessment of photogrammetric mapping accuracy based on variation ground control points number using unmanned aerial vehicle","volume":"95","year":"2017","journal-title":"Measurement"},{"key":"ref_58","doi-asserted-by":"crossref","unstructured":"Oniga, V.-E., Breaban, A.-I., and Statescu, F. (2018). Determining the Optimum Number of Ground Control Points for Obtaining High Precision Results Based on UAS Images. Proceedings, 2.","DOI":"10.3390\/ecrs-2-05165"},{"key":"ref_59","doi-asserted-by":"crossref","first-page":"04019007","DOI":"10.1061\/(ASCE)SU.1943-5428.0000283","article-title":"Assessment of GCP Number and Separation Distance for Small UAS Surveys with and without GNSS-PPK Positioning","volume":"145","author":"Bolkas","year":"2019","journal-title":"J. Surv. Eng."},{"key":"ref_60","doi-asserted-by":"crossref","unstructured":"Oniga, V.-E., Breaban, A.-I., Pfeifer, N., and Chirila, C. (2020). Determining the suitable number of ground control points for UAV images georeferencing by varying number and spatial distribution. Remote Sens., 12.","DOI":"10.3390\/rs12050876"},{"key":"ref_61","unstructured":"(2021, April 19). Pix4Dmapper\u2014Pix4D 2021. Available online: https:\/\/www.pix4d.com\/product\/pix4dmapper-photogrammetry-software."},{"key":"ref_62","doi-asserted-by":"crossref","unstructured":"Kyriou, A., Nikolakopoulos, K., and Koukouvelas, I. (2021). How image acquisition geometry of UAV campaigns affects the derived products and their accuracy in areas with complex geometry. ISPRS Int. J. Geo.-Inf., 10.","DOI":"10.3390\/ijgi10060408"},{"key":"ref_63","unstructured":"FGCD\u2014Federal Geographic Data Committee (1998). Geospatial Positioning Accuracy Standards. FGDC-STD-007.3\u20131998. Part 3: National Standards for Spatial Data Accuracy (NSSDA), Federal Geographic Data Committee Secretariat c\/o U.S. Geological Survey."},{"key":"ref_64","doi-asserted-by":"crossref","first-page":"591","DOI":"10.1093\/biomet\/52.3-4.591","article-title":"An analysis of variance for normality (complete samples)","volume":"52","author":"Shapiro","year":"1965","journal-title":"Biometrika"},{"key":"ref_65","doi-asserted-by":"crossref","first-page":"1","DOI":"10.2307\/2331554","article-title":"The probable error of a mean","volume":"6","author":"Sealy","year":"1908","journal-title":"Biometrika"},{"key":"ref_66","doi-asserted-by":"crossref","first-page":"80","DOI":"10.2307\/3001968","article-title":"Individual comparison by ranking methods","volume":"1","author":"Wilcoxon","year":"1945","journal-title":"Biom. Bull."},{"key":"ref_67","unstructured":"RStudio Team (2016). RStudio: Integrated Development for R, RStudio Inc."},{"key":"ref_68","doi-asserted-by":"crossref","first-page":"11933","DOI":"10.3390\/rs70911933","article-title":"The impact of the calibration method on the accuracy of point clouds derived using unmanned aerial vehicle multi-view stereopsis","volume":"7","author":"Harwin","year":"2015","journal-title":"Remote Sens."},{"key":"ref_69","unstructured":"Przybilla, H.-J., and B\u00e4umker, M. (2020, January 10\u201314). RTK and PPK: GNSS-Technologies for Direct Georeferencing of Uav Image Flights. Proceedings of the FIG Working Week 2020, Amsterdam, The Netherlands."}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/19\/3812\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T07:03:46Z","timestamp":1760166226000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/13\/19\/3812"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,9,23]]},"references-count":70,"journal-issue":{"issue":"19","published-online":{"date-parts":[[2021,10]]}},"alternative-id":["rs13193812"],"URL":"https:\/\/doi.org\/10.3390\/rs13193812","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2021,9,23]]}}}