# 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 c c} \hline \hline \multirow{2}{*}{**Device Mode**} & \multirow{2}{*}{**Signal Frequency**} & \multicolumn{4}{c}{**Canopy Openness**} \\ \cline{3-8}  & & **0.1–0.3** & **0.3–0.5** & **0.5–0.7** & **0.7–0.9** \\ \hline K9 & L1 & 29.35 \(\pm\) 1.88 b & 28.74 \(\pm\) 1.05 b & 30.46 \(\pm\) 1.21 a & 30.99 \(\pm\) 1.56 a \\  & L1 & 26.43 \(\pm\) 1.25 c & 26.42 \(\pm\) 0.80 c & 27.70 \(\pm\) 0.86 b & 28.64 \(\pm\) 1.26 a \\ NEO & L5 & 25.30 \(\pm\) 1.77 b & 26.15 \(\pm\) 1.50 b & 25.91 \(\pm\) 1.72 b & 27.74 \(\pm\) 1.03 a \\  & L1 & 28.87 \(\pm\) 1.27 c & 30.08 \(\pm\) 1.29 b & 30.56 \(\pm\) 0.69 b & 31.89 \(\pm\) 1.16 a \\ P50 & L5 & 28.41 \(\pm\) 1.25 b & 29.11 \(\pm\) 1.56 b & 29.30 \(\pm\) 1.71 b & 30.82 \(\pm\) 1.57 a \\ iRTK2 & L1 & 41.16 \(\pm\) 0.85 c & 41.28 \(\pm\) 0.79 c & 42.25 \(\pm\) 0.99 b & 43.48 \(\pm\) 1.56 a \\  & L5 & 41.29 \(\pm\) 1.09 c & 41.68 \(\pm\) 1.17 c & 42.57 \(\pm\) 0.78 b & 43.42 \(\pm\) 1.02 a \\ \hline \hline \end{tabular} Note: Different letters in the same row in the table indicate significant differences, where “\(\pm\)” represents the standard deviation.  
\end{table} 
Table 3: C/N0 of each device at different openness. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Device Mode**} & \multirow{2}{*}{**K9**} & \multirow{2}{*}{**NEO**} & \multicolumn{4}{c}{**P50**} & \multicolumn{4}{c}{**iRTK2**} \\ \cline{2-7}  & & **L1** & **L1** & **L5** & **L1** & **L5** & **L1** & **L5** \\ \hline Correlation coefficient & 0.492 & 0.641 & 0.363 & 0.625 & 0.392 & 0.601 & 0.591 \\ Significance & 0.001 & 0.001 & 0.006 & 0.001 & 0.003 & 0.001 & 0.001 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Correlation between C/N0 and canopy openness. Figure 9: Comparison of C/N0 of NEO, P50, and iRTK2 in L1 and L5 frequencies. Relationship between Canopy Openness and Positioning Accuracy in Single-Point Positioning (SPP) Mode  
Except for the recreational-grade device G138 BD, the positioning accuracy of each device improves with the increase in openness, as shown in Table 5 and Figure 10. The horizontal accuracy difference in G138 BD in various canopy openness is insignificant (\(p>0.05\)) and the rest of the device is generally stable when the canopy openness is more than 0.7. In Table 5, the errors in the east, west, and elevation directions are expressed as the root mean square error (RMS) and the errors in the horizontal direction are expressed as the distance root mean square error (DRMS). In general, when the canopy openness of the smartphone is greater than 0.7 in the east, north, and horizontal directions, the positioning accuracy is between 4.62 and 7.67 m. The positioning accuracy of dual-frequency mobile phones is better than that of single-frequency mobile phones in both horizontal and vertical directions. The precision of pseudo-range single-point positioning of survey-grade receivers is much higher than that of smartphones, which is about 3-8-times that of smartphones. When the canopy openness is greater than 0.7, it can reach sub-meter precision in east, north, and horizontal directions. The accuracy of recreational-grade devices is about 1.2-3-times that of smartphones and the average positioning accuracy in east, north, and horizontal directions is between 2.18 and 4.75 m. The influence of the difference in the original data quality of different devices on the positioning is more obvious in the elevation direction. The positioning accuracy of each device in the elevation direction is generally low and the error is about twice the positioning accuracy of the corresponding opening in the east or north direction.