## 2 Materials and Methods
### Evaluation Methods  
ArxMap 10.8 and Office Excel 2016 were used for final processing and creating a database. Since each pixel is of small dimensions, the same positions were used in terms of X and Y coordinates, and only the values of the Z coordinates, i.e., the values of the absolute heights, were compared. In ArcMap 10.8, the raster DTM and DSM overlapped with the GNSS points, the rasters of DTM and DSM were extracted only in the positions of GNSS points, and the maximum horizontal deviations between the GNSS points and the center of gravity of the raster were within 5 mm, which is a negligible error for forest land. Moreover, since the longitudinal profile of the forest/skid road is of interest, only the Z coordinate is important. The height data compared are between reference heights obtained by the GNSS device and data calculated from DTM and DSM obtained from UAV data processed in Pix4 Dmapper.  
The data are statistically processed to determine the reliability of the measurement for the method of determining the longitudinal slope of the forest/skid road. Based on the results of statistical processing, decisions are made on further processing and the use of the obtained data to confirm or refute research hypothesis 1. For statistical analyses, the Statistica 10 program was used. An analysis of variance of repeated measurements was performed, and a post hoc Tukey HSD test was conducted to assess statistical differences  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Processing of UAV Footage** \\ \hline \multirow{2}{*}{Camera model and image resolution} & FC6310, 8.8 \\  & 5472 \(\times\) 3648 (RGB) \\ \hline The shape of the flight mission’s recording grid & Double grid (for 3D models) \\ \hline \multirow{2}{*}{Planned distance between pixels according to the pix4 dcapture program (recording height of 50 m)} & 1.66 cm/px \\ \hline Actual pixel pitch (GSD) & 1.77 cm/px \\ \hline Covered area & 0.136 km\({}^{2}\)/13.6 ha \\ \hline Number of calibrated photos & 680 of 681 \\ \hline Number of 3D points in the point cloud & 68,093,217 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Parameters of the processed footage of the UAV device.  
Figure 4: Processing results of UAV recording (from left: orthomosaic, DTM, and DSM).  
between repeated measurements with different methods. If hypothesis 1 is confirmed, the project of the forest/skid road is created in the forest/skid road design program CESTA (a noncommercial program for designing forest/skid roads used in state services that manage forests in Croatia and produced in Slovenia by the company SOFDATA), to form the level of the planned road and to be able to compare the data with respect to whether an identical level can be formed based on these data. From these procedures, the values of the longitudinal slopes of the level breaks are obtained. Differences in the elevation of the level and the terrain for the results are checked in Statistics 10 with a T-test to determine whether there is a difference in the middle points of the road.  
To confirm or refute hypothesis 2, a design of the forest/skid road (re)construction based on data obtained from GNSS devices is created due to the assumption that data obtained by the UAV can be used in the future for a detailed construction or reconstruction project with respect to forest/skid roads. The project was later developed based on field data obtained using UAV devices, and earthwork data with respect to Fill and Cut (in cubic meters) were compared between each profile of the designed forest/skid road. The statistical comparison was performed with a T-test of the dependent variables.