# GNSS-Based Vertically Monitoring of Super-Tall Buildings
## 5 Verticality Monitoring Result and Analysis of the W Tower  
### Horizontal Motion Analysis of the W Tower  
The Guangzhou International Finance Center (denoted as the W Tower) is a reinforced concrete structure located in city center of Guangzhou, China. The building is a core tube structure and has a total height of 438 m. However, motion of the W Tower in a horizontal plane will occur due to such external factors as tower crane operation, wind, construction load, temperature, and sun exposure during construction. In this case, it is very necessary to analyze the impact of the W Tower's motion on laser plumbing. In order to obtain the motion of the W Tower, the coordinate time series of the monitoring point need to be calculated. The authors chose point WT (W Tower, the average of the plumbing points) as the monitoring station on the roof of the W Tower. In order to reduce the impact of the W Tower's motion on the vertical reference transmission, the reference point is first transmitted by the laser plummet at different moments. Then, the authors chose the average of plumbing points as the monitoring point WT. In addition, three points (HG, LYW, and ZT) are chosen from five construction control points to establish a reference network around the W Tower as shown in Figure 6. The authors chose \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \multicolumn{2}{c}{\(\mathbf{xyH}\) Direction (without Processing)} & \multicolumn{2}{c}{\(\mathbf{xyH}\) Directions (after Processing)} \\ \hline  & \(\mathbf{V_{x}}\) & \(\mathbf{V_{y}}\) & \(\mathbf{V_{H}}\) & \(\mathbf{V_{x}}\) & \(\mathbf{V_{y}}\) & \(\mathbf{V_{H}}\) \\ \hline \(<\)0.5 cm & 89.01 & 61.12 & 19.56 & 89.26 & 61.12 & 20.26 \\
0.5–1 cm & 10.94 & 34.13 & 19.54 & 10.74 & 34.24 & 20.45 \\
1–2 cm & 0.05 & 4.71 & 35.36 & 0 & 4.64 & 36.60 \\
2–3 cm & 0 & 0.04 & 17.88 & 0 & 0 & 16.87 \\ \(\geq\)3 cm & 0 & 0 & 7.66 & 0 & 0 & 5.82 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Statistics of differences in position in relation to the coordinate time series of the monitoring point (%). Figure 5: Differences in position in relation to the coordinate time series of the monitoring point: (a) \(x\) direction; (b) \(y\) direction; (c) \(H\) direction. these locations based on their suitability as reference stations according to the International GNSS service (IGS) criteria, keeping in mind the difficulty of finding adequate locations in an urban setting. Three control points were located on the concrete buildings as low as 100 m. Dual-frequency Trimble R8 GNSS receivers were placed at all stations to collect 24 h and 23 min data with a sampling rate of 0.067 Hz. The GNSS data of the reference network consisting of points HG, ZT, and LYW was firstly processed in the static mode to obtain the baseline vectors between reference stations. Secondly, the GNSS data of the monitoring station, namely WT, was processed in the post-processed kinematic mode to obtain baseline vectors from the monitoring station to each reference station, giving a total of 13,495 baseline vectors at 5648 epochs. Among others, there are 659 single baselines, which means only one baseline vector can be successfully calculated between the monitoring station and one of the three reference stations at 659 epochs. In particular, the 659 baseline vectors will be used directly without any processing in the following. Owing to observational conditions, the integer ambiguity resolution cannot be fixed at 206 epochs. Thirdly, the monitoring network was constructed by the reference network and the baseline vectors between the monitoring station and reference stations at each epoch. Then, the authors check the misclosures and the corrections of baseline vectors to identify and eliminate gross errors of baseline vectors epoch-by-epoch. By checking the misclosures and the corrections of baseline vectors, total of 1726 baseline vectors are eliminated as gross errors.