## 3 Results  
### Assessment of the Positioning Accuracy of the Trimble R12 GNSS Receiver Mounted on a Harvester  
The easting and northing positions obtained from the Trimble R12 GNSS receiver were compared with the true positions obtained from the total station, which allowed for the calculation of deviations. As stated, the Trimble R12 has a maximum horizontal precision of 8 mm, according to its product specification [28]. The 8 mm threshold was thus used to classify the positions as either 'Accurate' or 'Inaccurate'. From the total of 5564 observations obtained, 751 were identified as 'Inaccurate', meaning that the Trimble R12 was able to achieve the maximum horizontal precision of 8 mm for the remaining 4813 observations (86% of all observations). The spatial distribution of the classified positions is illustrated in Figure 4, while Table 2 displays the geometric quality of the GNSS signals used to determine the positions. A further analysis of the geometric quality of the GNSS signals showed that, on average, fewer satellites were available to determine the positions for the 'Inaccurate' class positions. A paired-samples \(l\)-test was conducted to compare differences in the number of satellites, GDOP, PDOP, VDOP, and HDOP for 'Accurate' and 'Inaccurate' positions. There was a significant difference in the number of satellites, GDOP, PDOP, VDOP, and HDOP for 'Accurate' and 'Inaccurate' positions. These results suggest that the numbers of satellites were higher for the 'Accurate' positions than for the 'Inaccurate' positions. The values of GDOP, PDOP, VDOP, and HDOP were smaller for the 'Accurate' positions than for the 'Inaccurate' positions. This disparity is likely due to the canopy's impact on the GNSS equipment installed on the roof of the harvester. The results indicate that the Trimble R12 GNSS receiver can provide a high level of positioning accuracy with a reasonably good availability; although, the presence of a forest canopy may negatively affect its performance. Figure 4: Spatial distribution of the classified measured positions using the Trimble R12 GNSS receiver mounted on a harvester. The Effect of Canopy Cover on the Position Accuracy of the Trimble R12 as Evaluated by Analyzing the Canopy Height Model  
The impact of canopy cover on the positional accuracy of the Trimble R12 was evaluated using a CHM. The CHM was reclassified to exclude pixels located below the Trimble R12 by using the height of the harvester roof as a reference (Figure 5). The results show that the mean canopy cover was higher for 'Inaccurate' points than for 'Accurate' points (Table 3). However, there were points that were correctly positioned even with the presence of a high level of canopy cover (86%). A paired-samples \(t\)-test was conducted to compare differences in the canopy cover estimated from the canopy height model for 'Accurate' and 'Inaccurate' positions. There was a \begin{table}
\begin{tabular}{l l l l l l l l l} \hline
**Variable** & \multicolumn{2}{l}{**’Accurate’ (n = 4813)**} & \multicolumn{3}{l}{**’Inaccurate’ (n = 751)**} & **t** & **df** \\ \hline  & **Mean** & **Std. dev.** & **Range** & **Mean** & **Std. dev.** & **Range** & & \\ \hline Number of GLONASS satellites & 3.90 & 1.27 & 0–7 & 3.23 & 1.07 & 1–6 & 15.30 & 1103 \\ Number of GPS satellites & 7.35 & 1.59 & 2–10 & 6.93 & 1.54 & 2–10 & 6.85 & 1015 \\ Number of all satellites & 11.25 & 2.26 & 5–17 & 10.17 & 1.98 & 5–14 & 13.62 & 1079 \\ Geometric dilution of precision (GDOP) & 3.00 & 1.42 & 1.6–17.3 & 3.47 & 1.98 & 1.8–16.5 & \(-\)6.81 & 875 \\ Position dilution of precision (PDOP) & 2.25 & 1.00 & 1.2–12 & 2.60 & 1.38 & 1.4–11.9 & \(-\)6.79 & 877 \\ Vertical dilution of precision (VDOP) & 1.96 & 0.88 & 1–10.9 & 2.29 & 1.24 & 1.2–11.3 & \(-\)7.00 & 870 \\ Horizontal dilution of precision (HDOP) & 1.07 & 0.52 & 0.6–9.1 & 1.19 & 0.65 & 0.7–6.4 & \(-\)4.95 & 907 \\ \hline \end{tabular}
\end{table}