## 2 Materials and Methods
### Data Processing  
The number of images used for each site are presented in Table 1. The images were processed with Pix4 Dmapper (Version 4.6.4) by Pix4D [61]. For each site, we carried out two separate processing procedures, following the georeferencing methods: (a) processing by carrying out BBA_traditional and (b) processing by carrying out BBA_PPK. For the latter, a geolocation file was used to add the coordinates to the perspective centers of the images, while, for the former, the geolocation data of images were removed. The coordinate system used for the horizontal geodetic datum was Slovenia 1996/Slovene National grid with Slovenian Geodetic Datum 1996, while that for the vertical was the EGM96 Geoid model. The configuration of processing parameters was the same under all georeferencing methods: initial processing was performed in full mode; for point cloud densification, we used an image scale of 1/2 (i.e., half image size) and high point density; and the additional photogrammetric products were orthomosaic and DSM (Figure 5).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Location** & **Area Surveyed** & **Georeferencing** & **Cameras** & **Key Points per** & **Dense Cloud** & **Orthomosaic,** **DSM Resolution** \\ \hline \multirow{4}{*}{KEKEC} & \multirow{4}{*}{3.4} & BBA\_traditional & \multirow{4}{*}{135/135} & \multirow{4}{*}{65,326} & 45,662,559 & \multirow{4}{*}{2.4} \\  & & BBA\_PPK & & & (327.6/m\({}^{3}\)) & \\ \cline{1-1} \cline{5-6}  & & BBA\_PPK & & & 45,754,260 & \\ \cline{1-1} \cline{5-6}  & & BBA\_traditional & \multirow{4}{*}{659/659} & \multirow{4}{*}{69,863} & 159,285,721 & \multirow{4}{*}{2.5} \\  & & BBA\_PPK & & & (836.51/m\({}^{3}\)) & \\ \cline{1-1} \cline{5-6}  & & BBA\_PPK & & & 165,097,231 & \\ \cline{1-1} \cline{5-6}  & & BBA\_traditional & \multirow{4}{*}{368/368} & \multirow{4}{*}{72,809} & 100,688,038 & \multirow{4}{*}{2.2} \\ \cline{1-1} \cline{5-6}  & & BBA\_PPK & & & (1635.12/m\({}^{3}\)) & \\ \cline{1-1} \cline{5-6}  & & BBA\_PPK & & & 106,209,704 & \\ \cline{1-1} \cline{5-6}  & & & & (1707.94/m\({}^{3}\)) & \\ \hline \hline \end{tabular}
\end{table}
Table 1: Results of photogrammetric processing provided by the Pix4D software for different locations and georeferencing methods.  
The precision values of the perspective centers of coordinates for BBA_PPK method are given in Table 2, while they were not needed for BBA_traditional, as all positional data of the images were removed before the processing.  
The resolution of orthomosaic and DSM was determined to be the same as the GSD (Kekec, 2.4 \(\times\) 2.4 cm; Krnica, 2.5 \(\times\) 2.5 cm; and Mangart, 2.2 \(\times\) 2.2 cm; Table 1). For the creation of the DSM, we used default options in Pix4 DMapper, namely noise filtering to correct the altitude of points with the median altitude of neighboring points, as well as sharp  
was generated by using these points. However, the surface can still contain areas with erroneous small bumps, and with surface smoothing these areas are then corrected by flattening. Sharp surface smoothening is by default, and this type of smoothening tries to preserve the orientation of the surface, and keeps sharp objects. In this process, only quasi-planar areas were flattened. The DSM was generated in the raster GeoTIFF file format, using the method of inverse distance weighting. The results of photogrammetric processing are provided in Figure 5.