# Evaluation of Positioning Accuracy of Smartphones under Different Canopy Openness
## 3 Results
### Correction of Raw Location Data of Smartphone by PPP Mode  
After correcting by PPP mode, the survey-grade receiver iRTK2 still has the highest accuracy among all devices (Table 6). In the east and north directions, when the canopy openness is between 0.1 and 0.7, the smartphone can reach a positioning accuracy of about 3 m. When the canopy openness is greater than 0.7, it can reach positioning accuracy of about 1.5 m. Overall, it is better than the recreational-grade receiver G138 BD. The measurement-level devices can maintain sub-meter accuracy under each canopy openness. In the horizontal direction, when the canopy openness is between 0.1 and 0.7, the smartphone can reach the positioning accuracy within 5 m and the measurement-level devices can reach the positioning accuracy within 1.5 m; when the canopy openness is greater than 0.7, the smartphone can reach positioning accuracy of about 2.5 m and the measurement-level devices can reach the sub-meter accuracy. In addition, compared with SPP mode, the variation trend in each device with the openness in PPP mode is weakened. The horizontal positioning accuracy of devices in each opening range is mostly not significantly different (\(p>0.05\)). In the horizontal direction, under the PPP mode, the average positioning accuracy of each openness range of the smartphone can reach within 5 m. Under the high-opening environment (0.7-0.9), the average positioning accuracy can reach within 3 m.  
The relationship between canopy openness and plane positioning accuracy by PPP mode is shown in Figure 11. Compared with pseudo-range single-point mode, its R2 of the fitting equation of the positioning accuracy varies with openness decreases. The main reason is that the greater the error and the better the data quality, the more obvious the accuracy improvement in the PPP mode. As a result, the positioning accuracy tends to weaken with the canopy openness, so the accuracy of measuring points in the figure is more dispersed than that of the SPP mode. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Error** & **Device** & \multicolumn{4}{c}{**Canopy Openness**} \\
**Direction** & **Mode** & **0.1–0.3** & **0.3–0.5** & **0.5–0.7** & **0.7–0.9** \\ \hline \multirow{4}{*}{East direction (m)} & K9 & 1.94 \(\pm\) 1.47 a & 2.45 \(\pm\) 2.10 a & 2.16 \(\pm\) 1.85 a & 1.53 \(\pm\) 1.66 a \\  & NEO & 3.48 \(\pm\) 2.53 b & 2.60 \(\pm\) 1.73 ab & 3.04 \(\pm\) 2.17 b & 1.40 \(\pm\) 1.60 a \\  & F50 & 1.85 \(\pm\) 1.74 ab & 1.89 \(\pm\) 1.44 b & 1.07 \(\pm\) 0.87 a & 1.29 \(\pm\) 0.78 ab \\  & iRTK2 & 0.80 \(\pm\) 1.02 a & 0.70 \(\pm\) 0.54 a & 0.46 \(\pm\) 0.37 a & 0.40 \(\pm\) 0.38 a \\  & K9 & 3.45 \(\pm\) 1.85 ab & 3.77 \(\pm\) 3.03 b & 3.36 \(\pm\) 2.81 ab & 1.69 \(\pm\) 1.64 a \\  & NEO & 2.07 \(\pm\) 1.30 a & 2.92 \(\pm\) 2.18 a & 3.16 \(\pm\) 2.38 a & 1.73 \(\pm\) 1.41 a \\  & P50 & 2.86 \(\pm\) 2.16 b & 1.79 \(\pm\) 0.97 ab & 1.48 \(\pm\) 1.37 a & 2.17 \(\pm\) 1.61 ab \\  & iRTK2 & 0.87 \(\pm\) 0.46 a & 0.84 \(\pm\) 0.85 a & 0.82 \(\pm\) 0.45 a & 0.59 \(\pm\) 0.53 a \\  & K9 & 4.43 \(\pm\) 3.52 a & 4.10 \(\pm\) 4.24 a & 4.84 \(\pm\) 4.55 a & 2.51 \(\pm\) 3.54 a \\  & NEO & 3.02 \(\pm\) 1.93 a & 3.77 \(\pm\) 2.53 a & 3.75 \(\pm\) 2.55 a & 3.94 \(\pm\) 2.22 a \\  & F50 & 1.59 \(\pm\) 0.89 b & 4.62 \(\pm\) 2.55 a & 4.67 \(\pm\) 3.27 a & 4.16 \(\pm\) 3.42 ab \\  & iRTK2 & 1.23 \(\pm\) 1.07 a & 1.74 \(\pm\) 1.38 a & 1.90 \(\pm\) 1.52 a & 2.27 \(\pm\) 1.78 a \\  & K9 & 4.10 \(\pm\) 2.04 ab & 4.66 \(\pm\) 3.45 b & 4.50 \(\pm\) 2.58 b & 2.69 \(\pm\) 1.80 a \\  & NEO & 4.24 \(\pm\) 2.48 b & 4.23 \(\pm\) 2.22 b & 4.61 \(\pm\) 2.84 b & 2.43 \(\pm\) 1.88 a \\  & P50 & 3.96 \(\pm\) 1.67 b & 2.82 \(\pm\) 1.33 ab & 2.01 \(\pm\) 1.37 a & 2.69 \(\pm\) 1.50 ab \\  & iRTK2 & 1.35 \(\pm\) 0.85 b & 1.25 \(\pm\) 0.80 b & 1.01 \(\pm\) 0.44 ab & 0.75 \(\pm\) 0.60 a \\ \hline \hline \end{tabular} Note: Different letters in the same row in the table indicate significant differences, where “\(\pm\)” represents standard deviation.  
\end{table}