## 3 Milano Test Processing and Analysis  
The data of the Milano Test were acquired and courteously provided by Riccardo Barzaghi and Mirko Reguzzoni, Department of Civil and Environmental Engineering, Politecnico di Milano. The dataset is relevant to a short baseline (approximately 65 m long) formed by the permanent station (Topcon Odyssey RS) of Politecnico di Milano--Milano Leonardo Campus and one u-blox LEA-4T. Both receivers were mounted on the roof of a building owned by Politecnico, at about 24 m above ground level: the acquisition site was already used in several previous geodetic tests and offers an optimal observation environment. The survey lasted one week, from 14 to 20 March 2014 (respectively, days of the year--DOY 073 and 079). Our analysis of Milano data is mainly aimed at a first assessment of potential accuracies reached by low-cost receivers.  
Firstly, we processed the whole week with BSW5.2 to estimate a reference position of the rover. Then, the hourly sessions were processed to estimate the rover positions: the time series of the residuals relative to the reference position were finally computed:  
\[\delta\mathbf{x}_{i}=\mathbf{x}_{i}-\mathbf{\overline{x}} \tag{1}\]  
where \(\mathbf{\overline{x}}\) is the reference position of the rover, \(\mathbf{x}_{i}\) is the estimated position for session \(i\), and \(\delta\mathbf{x}_{i}\) is the vector of the residuals. The residuals are presented as local east, north, and up with respect to the reference position.  
In total, 168 results were obtained. Five (3%) were clearly blundered: Table 2 presents their three dimensional (3D) residuals.  
The statistics for the other sessions are presented in Table 3. Overall, the results are completely satisfactory: the root mean square error (RMSE) of the solutions is 2.1 mm for east, 4.9 mm for north, and 4.5 mm for up directions.  
\begin{table}
\begin{tabular}{c c c} \hline
**Parameter** & **BSW5.2** & **LGO** \\ \hline Observables & GPS L1 phase observations & GPS L1 phase observations \\ Differencing level & double & double \\ Session length & 1 h & 1 h \\ Troposphere & Saastamoinen & Saastamoinen \\ Elevation cut-off & 10\({}^{\circ}\) & 10\({}^{\circ}\) \\ Ambiguity resolution & SIGMA & yes \\ \hline \end{tabular}
\end{table}
Table 1: BSW5.2 and LGO processing parameters (only main parameters are shown).  
height estimates. In Table 6 it can be seen that both horizontal and vertical residuals do not pass 15 mm for almost all sessions in the case of both software. There are only four exceptions: for BSW5.2 one session (0.6%) for east and two sessions for north, and for LGO only one session for north.  
Finally, a graphical comparison between LGO and BSW5.2 residuals is presented in Figures 1-3. Just for a better visual inspection, three residuals that exceed the interval [\(-\)2.0 cm, \(+\)2.0 cm] have been removed from the graphs: two for BSW5.2 and one for LGO. Almost all the other residuals show similar magnitude and sign for almost all the sessions and a daily period appears, in particular for the height: this is probably caused by multipath interference, particularly significant for low-cost antennas.  
In conclusion, we had five (BSW, Table 2) plus four (LGO, Table 4) blundered results, which seems to be a relatively big number. These blunders are mainly caused by occasional problems in the data but probably also because of another reason: packages for post-processing of GNSS static sessions are optimized for data acquired by geodetic receivers and not for low-cost receivers. Other, and more detailed, results relevant to the Milano test are discussed in [30].