# Assessment of GNSS Galileo Contribution to the Modernization of CROPOS's Services
## 4 Discussion
### Analysis and Discussion of the VPPS Results  
In general, a box and whisker chart shows a distribution of data into quartiles, highlighting the mean and outliers [71]. The interquartile range (IQR) measures the spread of the middle half of the data [41]; it is the range for the middle 50% of the data sample [72]. The lowest quartile (Q1) covers the smallest quarter of values in the dataset, and the upper quartile (Q4) comprises the highest quarter of values. The interquartile range is the middle half of the data that lies between the upper and lower quartiles. In other words, the interquartile range includes the 50% of data points that are above Q1 and below Q4. Unlike the more familiar mean and standard deviation, the interquartile range and the median are more robust measures. By comparing the size of the boxes, the variability of the data in the dataset can be understood: more dispersed distributions have wider boxes. A total number of 27 VPPS (GGG) results gained through 9 sessions (27 = 9 \(\times\) 3) using GGG observations along with the almost simultaneous 26 VPPS (GAL) results gained through 9 sessions (26 = 9 \(\times\) 3 \(-\) 1) have enabled the box and whisker plots of Easting,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \multirow{2}{*}{**Session**} & \multicolumn{2}{c}{**Number**} & \multirow{2}{*}{**Time (CET)**} & \multirow{2}{*}{**Number of SV**} & \multicolumn{2}{c}{**Number**} & \multirow{2}{*}{**Time**} & **Number** & \multirow{2}{*}{**Time (CET)**} \\  & & & & **(RINEX)**: GAL & & **VPPS** & **(CET)** & **VPS** \\ \hline
2. & 6 + 4 + 6 - 16 & 08:25 & 6 & 17 & 08:12 & 5 & 08:22 \\ \hline
3. & 8 + 5 + 6 - 19 & 09:38 & 6 & 16 & 09:3  
Northing, and Height components. The results obtained with VPPS (GGG) and VPPS (GAL-only) observations are compared with the REFERENCE (REF) and shown in Figure 13 (Easting, Northing, Height). Analysis and interpretation of results shown in Figure 13 are provided for Easting, Northing, and Height components as follows:  
* Easting (Figure 13, left). The range of the Easting results obtained by GGG and 'GAL-only' are 0.0095 m and 0.0081 m, respectively. The greater range for GGG is due to the results obtained in session A-6 having higher DOP values (see Figure 9). The IQR for GGG solution is a bit higher (0.0056 m) compared to the 'GAL-only' solution (0.0054 m). Interestingly, the median values are almost equal (0.2 mm of difference), whereas there is a small difference between the average values of GGG (0.0176 m) vs. 'GAL-only' (0.0184). Both median values compared to the REF value supply the differences of 0.0009 m and 0.0011 m (GGG vs. 'GAL-only'), which can be considered as a negligible amount. The averaging of VPPS results provides a more accurate and reliable solution. Easting components obtained with GGG and GAL-only observations have shown a great level of similarity (matching), leading to the conclusion that Easting components obtained with 'GAL-only' observations can be regarded as equally accurate and reliable as those obtained with GGG observations. * Northing (Figure 13 middle). There is a small difference between median values: GGG (0.0276 m) vs. GAL-only (0.0277 m). There is a small difference between the average values: GGG (0.0273 m) vs. GAL-only (0.0270 m). The IQR is slightly smaller for GGG (0.0039 m) vs. GAL-only (0.0041 m), but the range for GAL-only is bigger (0.0114 m) compared to GGG (0.0076 m). That means that there is a higher spread of the results obtained with GAL-only observations, which can be seen in STDEV values, as well (0.0021 m vs. 0.0026 m). The higher range for Northing components obtained with GAL-only comes from the results in session A-8 (see Figure 10).