## 3 Results and Discussion
### Post-Processing Approach  
As previously stated, the first tests were made with consideration for single baseline positioning that was obtained with a CORS and various VR (changing the inter-station distance between virtual stations and rover along with different session lengths) in a post-processing approach. Some interesting results were obtained that are described as follows:  
The first experiment corresponded to the CORS post-processing approach: we used a real permanent station eight km from the rover. Data were acquired simultaneously using the same antenna (Garmin GA38) connected to the splitter using a sampling rate of 1 s. The average values of Position Dilution of Precision (PDOP) were approximately 1.2. As stated, the results were obtained in the \"single base\" mode using commercial software (Leica Geomatics Office(tm) v.8.3 by Leica Geosystems(r)). As seen in Table 3, both NVS and u-blox receivers can fix the phase ambiguity of a session length equal to five minutes while for a longer session (ten minutes) only the double constellation receiver was able to fix the phase ambiguity. Analysing the results, a strange behaviour in the last receiver is observed. In this last case (session length of five minutes) despite the phase ambiguity being fixed, it is noted that the results are incorrect: the planimetric coordinates are approximately 66 cm from the \"true\" coordinates (where \"true\" means the adjusted coordinates obtained with the Bernese 5.0 software in the post-processing approach using two geodetic receivers) while the altimetry difference is about 1.6 m! On the other hand, the u-blox receiver is not able to fix the phase ambiguity but provides better results. The difference between the \"true\" and estimated coordinates is about 9 cm using the planimetric components and only two cm for the altimetric ones. The results in terms of the differences between \"true\" and estimated coordinates are shown in Table 2.  
It should be noted that with the NVS receiver and five minutes of data, the software declares to have reached ambiguity fixing, but only for GPS measurements. These ambiguity values are clearly incorrect. We have also performed these type of tests in different days (12 sessions in 5 days), \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**NVS (Garmin Antenna, GPS + GLONASS)**} \\ \hline  & \(\mathbf{\mu E}\) **[m]** & \(\mathbf{\mu N}\) **[m]** & \(\mathbf{\mu h}\) **[m]** & \(\mathbf{\sigma E}\) **[m]** & \(\mathbf{\sigma N}\) **[m]** & \(\mathbf{\sigma h}\) **[m]** & \\ \hline
5 min & 0.004 & 0.655 & \(-1.599\) & 0.012 & 0.019 & 0.026 & FIX GPS \\
10 min & \(-0.011\) & 0.015 & 0.029 & 0.008 & 0.011 & 0.019 & FIX GPS \\ \hline  & \multicolumn{6}{c}{**u-blox (Garmin Antenna, only GPS)**} \\ \hline  & \(\mathbf{\mu E}\) **[m]** & \(\mathbf{\mu N}\) **[m]** & \(\mathbf{\mu h}\) **[m]** & \(\mathbf{\sigma E}\) **[m]** & \(\mathbf{\sigma N}\) **[m]** & \(\mathbf{\sigma h}\) **[m]** & \\ \hline
5 min & 0.002 & 0.006 & 0.020 & 0.003 & 0.002 & 0.008 & FIX \\
10 min & \(-0.084\) & \(-0.050\) & 0.022 & 0.011 & 0.018 & 0.012 & FLT \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Differences between “true” and estimated coordinates of NVS (**Top**) and u-blox (**Bottom**) receivers using a CORS eight km from the rover. considering also different hours (night and day) in order to analyse the results also in terms of number of visible satellites and atmospheric conditions: in Table 3 are shown the main statistical parameters that represent the obtained results. We have computed the accuracy considering the 95% of significance level, in order to have a complete analysis from a statistical point of view. If we consider the NVS receiver, comparing Tables 3 (top) and 4 no substantial differences can be found except for the fixing of the phase ambiguity that is not reached. Despite this, in these experiments the accuracy and precisions are comparable both for the u-blox and the double constellation receiver.