## 4 Discussion  
If six baseline vectors and the original APPS algorithm were used, the mean distance of the determined position of the BROD station to the reference position was 0.018 m, while, for the proposed modification with the UAM, it was 0.015 m. The distance coefficient of variation was reduced to 61% from 70%. For OPOC, the mean distance from the positions determined with the APPS to the reference position was 0.016 m. Using the proposed modification, we achieved 0.012 m. The distance coefficient of variation was then reduced to 62% from 94% in this case. The mean distance from the determined positions of JASL to its reference positions was 0.018 m for APPS; for the modified approach, it was 0.013 m. Additionally, in this case, the distance coefficient of variation was reduced to 85% from 155%. Figure 6: Time series of geometrical height differences with respect to the reference values of the analysed points for EAM (black) and UAM (cyan) using baseline vectors to the six and five nearest ASG-EUPOS stations. The percentage of positions within 0.02 m of the reference positions varied from 66% to 76% for the EAM with six baseline vectors, while, for the UAM, it amounted to between 80% and 89% (Figure 7). The UAM and five baseline vectors yielded the most precise results (Figure 7). Therefore, the proposed modification improves service precision. The mean distance of BROD to its reference position was 0.015 m for the EAM and five baseline vectors and 0.014 m for the UAM. The distance coefficient of variation was reduced to 58% from 82%. When we used five vectors and the EAM, the mean distance to the reference position of the OPOC station was 0.012 m, while, with the UAM, it was 0.011 m. The distance coefficient of variation for OPOC declined to 66% from 101%. For five baseline vectors and the EAM adjustment, the mean distance of JASL to the reference position was 0.016 m, which changed to 0.012 m when the UAM was applied. The positioning distance coefficient of variation was reduced to 97% from 214% for JASL. A distance coefficient above 100% indicates that the value of the standard deviation of vector length deviations exceeds the mean value, which proves the presence of outliers in the solution set. Accuracy measures for 3D positioning for sets of positions indicated an improvement in accuracy when the UAM was applied (Figure 8). MRSE, SAS90, and SAS99 were the lowest for each analysed point when the proposed modification was employed with the UAM and five baseline vectors. The accuracy measures also improved when the UAM was used with six baseline vectors for BROD and OPOC. When the APPS of the ASG-EUPOS employed the current EAM with five vectors, the accuracy measures for the analysed points improved as well. The current AUSPOS service yields the mean linear discrepancy of 0.05 m for horizontal coordinates and 1 h static observations. When the session is extended to four hours, the planar mean linear discrepancies reach 0.02 m for AUSPOS and OPUS [6]. [PERSON] et al. [37] noted that the accuracy of the AUSPOS service and PPP automatic post-processing services such as APPS JPL or Trimble RTX increases significantly for 6 h satellite observations in good conditions. Mean differences in coordinates in relation to coordinates from Bernese 5.2 amount to between 0.001 and 0.013 m for N, 0.005 and 0.011 m for E, and 0.009 and 0.108 m for U in such a case [37]. Based on the analysis of the spatial distribution of the points positioned in relation to their reference positions in the horizontal plane, calculated mean linear discrepancies, and 2 DRMS, we can conclude with 95% probability that the horizontal plane accuracy for 1 h GPS observations is not worse than 0.03 m for the UAM  
Figure 7: Classification of 3D distances from determined positions to reference positions for the standard approach (EAM) and the proposed modification (UAM) by station. adjustment with six or five baseline vectors.