# Evaluation of Positioning Accuracy of Smartphones under Different Canopy Openness
## 3 Results
### Influence of Canopy Openness on the Number of Observation Satellites and Signal Quality
#### 3.1.2 Influence of Canopy Openness and Equipment on Carrier-to-Noise Density
\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{6}{*}{East direction (m)} & K9 & 8.36 \(\pm\) 4.38 b & 8.00 \(\pm\) 3.98 b & 6.70 \(\pm\) 2.48 b & 4.95 \(\pm\) 1.80 a \\  & NEO & 7.89 \(\pm\) 3.64 b & 7.02 \(\pm\) 2.36 b & 5.41 \(\pm\) 1.49 a & 4.70 \(\pm\) 2.00 a \\  & P50 & 5.71 \(\pm\) 1.12 a & 7.83 \(\pm\) 3.91 b & 5.47 \(\pm\) 2.17 a & 4.62 \(\pm\) 1.86 a \\  & G138 BD & 3.67 \(\pm\) 1.82 b & 2.88 \(\pm\) 1.20 ab & 2.38 \(\pm\) 0.82 a & 2.18 \(\pm\) 1.51 a \\  & iRTK2 & 1.35 \(\pm\) 0.84 b & 1.60 \(\pm\) 1.06 b & 1.06 \(\pm\) 0.51 ab & 0.63 \(\pm\) 0.39 a \\  & K9 & 7.99 \(\pm\) 1.91 b & 9.30 \(\pm\) 4.05 b & 7.61 \(\pm\) 1.78 b & 5.67 \(\pm\) 2.13 a \\  & NEO & 7.75 \(\pm\) 2.56 b & 8.42 \(\pm\) 2.58 b & 7.24 \(\pm\) 2.65 b & 5.03 \(\pm\) 2.23 a \\  & P50 & 6.90 \(\pm\) 2.18 b & 7.72 \(\pm\) 2.24 b & 6.92 \(\pm\) 2.61 b & 5.20 \(\pm\) 2.15 a \\  & G138 BD & 2.85 \(\pm\) 0.81 a & 3.53 \(\pm\) 0.90 a & 2.85 \(\pm\) 1.47 a & 3.36 \(\pm\) 1.55 a \\  & iRTK2 & 1.49 \(\pm\) 0.49 b & 1.61 \(\pm\) 0.73 b & 1.52 \(\pm\) 0.51 b & 0.86 \(\pm\) 0.54 a \\  & K9 & 16.72 \(\pm\) 6.10 ab & 18.19 \(\pm\) 7.91 b & 14.84 \(\pm\) 4.65 a & 13.03 \(\pm\) 5.80 a \\  & NEO & 14.42 \(\pm\) 5.25 a & 16.72 \(\pm\) 5.99 b & 16.45 \(\pm\) 4.76 b & 12.99 \(\pm\) 5.86 a \\  & P50 & 11.67 \(\pm\) 3.33 a & 16.95 \(\pm\) 5.44 b & 14.46 \(\pm\) 4.68 b & 11.18 \(\pm\) 3.90 a \\  & G138 BD & 13.10 \(\pm\) 1.68 bc & 12.99 \(\pm\) 2.36 c & 11.26 \(\pm\) 2.54 b & 9.48 \(\pm\) 2.31 a \\  & iRTK2 & 3.65 \(\pm\) 0.83 a & 3.76 \(\pm\) 1.62 a & 3.45 \(\pm\) 1.12 a & 2.79 \(\pm\) 1.56 a \\  & K9 & 11.91 \(\pm\) 3.61 b & 12.35 \(\pm\) 5.46 b & 10.28 \(\pm\) 2.50 b & 7.67 \(\pm\) 2.29 a \\  & NEO & 11.10 \(\pm\) 4.31 b & 11.03 \(\pm\) 2.17 b & 9.11 \(\pm\) 2.81 b & 6.96 \(\pm\) 2.81 a \\  & P50 & 9.03 \(\pm\) 2.07 ab & 10.51 \(\pm\) 2.80 b & 9.54 \(\pm\) 2.73 b & 7.04 \(\pm\) 2.09 a \\  & G138 BD & 4.75 \(\pm\) 1.66 a & 4.65 \(\pm\) 1.16 a & 3.89 \(\pm\) 1.18 a & 4.29 \(\pm\) 1.42 a \\  & iRTK2 & 2.08 \(\pm\) 0.78 b & 1.99 \(\pm\) 0.54 b & 1.85 \(\pm\) 0.67 b & 0.99 \(\pm\) 0.48 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} 
Table 5: Positioning accuracy of each device in single-point positioning (SPP) mode. There is a linear relationship between the openness and the plane positioning accuracy in the pseudo-range single-point mode (Figure 10). Both the survey-grade receiver iRTK2 and the recreational-grade receiver G138 BD can reach the meter accuracy level. However, the accuracy of G138 BD in the high-openness environment has not changed significantly compared with medium and low openness. This phenomenon is quite different from iRTK2. The reason may be that the data presented by G138 BD are not obtained in the original pseudo-range single-point positioning mode, which internal algorithms have processed, and the overall accuracy decreases with the environment. This phenomenon is similar to the effect of each device treated by the PPP method. The canopy openness under the forest has a great influence on the positioning accuracy of the device. Without any processing, only the survey-grade device can obtain relatively stable original positioning data, which has high positioning availability in forestry work. In SPP mode, the horizontal accuracy of smartphones is low and there are significant limitations in forestry work. Although the positioning accuracy of dual-frequency smartphones is improved compared with that of single-frequency smartphones, there is still a big gap compared with the survey-grade device, which can only meet the needs of recording the approximate location of sample plots or rough navigation in forest areas and playing an auxiliary role in forest land restoration. Suppose such work needs low positioning accuracy.