## 3 Results and Discussion
### Deviations of Positioning and Their Error Indicators from the Period \"FIX\"  
Another evaluation was performed on deviations from the period when the RTK receivers knew the integer value of the carrier phase (when in the \"FIX\" system state) and were measured in their most accurate mode. The graph (Figure 5) plots histograms of the density of the horizontal deviations from the MRA reference trajectory in latitude and longitude (north and east). The density of the deviations \(d_{i}\) from this period is further shown in Figure 6, together with the calculated error indicators (\(\mu_{err}\), \(s_{err}\) and \(RMS_{err}\)). The evaluation was largely influenced by the size of the \(n_{f}\) datasets. The size of the datasets was mainly affected by the \(SSR\) ratio of each of the receivers, as well as by the fact that Receiver D allowed samples with only four times lower frequency (5 Hz compared to 20 Hz). It must be noted that Receiver B also had a \"failure\" of the measurement section in these measurements, which is not shown in this view. This anomaly was also taken into account in the evaluation. Figure 5: The density of occurrence of the horizontal deviations from the reference trajectory of the MRA in the latitude and longitude of the four RTK receivers (**a–d**) from the measurement period “FIX”. The horizontal distribution of the deviations was plotted for the graph of each RTK receiver in the large square area at the bottom-left. The percentage ratio of the occurrence density of the deviation in the area was plotted using a colour scale in a linear normalised distribution (where: black = 0%, red = 50% and white = 100%). Furthermore, the narrow bar histograms on the right and top show the density of the occurrence of the deviation in latitude and longitude in units of the obtained samples. The density of all three views of each image was calculated identically for all the four receivers from the displayed range (\(-\)0.6 m to 0.6 m) in the number of 1000 bins (resolution 1.2 mm). The Receiver A error indicators were calculated from the largest dataset and showed worse values than Receiver C (worst performing in the previous evaluation) and Receiver D. Receiver A was also loaded with a positioning error that occurred immediately from the initial start-up of the first measuring set (specifically at speeds of 0.1-3.7 m s\({}^{-1}\) and an acceleration of 0.3-1.3 m s\({}^{-2}\)), when 98 samples showed a deviation of 0.45-0.54 m. Receiver B produced the worst result, as, during the period of one of the trolley starts (specifically at speeds of 0.1-7.9 m s\({}^{-1}\) and an acceleration of \(-\)0.2-1.2 m s\({}^{-2}\)), it measured a deviation of 4.9-5.1 m in 436 samples. Paradoxically, the smallest error indicators were displayed by Receiver C (the second-worst in the previous evaluation). Its largest deviations ranged from 0.1 m to 2.6 m in the number of 21 samples occurring in two periods at high speeds (specifically, at speeds of 7.9-8.4 m s\({}^{-1}\) and an acceleration of 0.6-2.6 m s\({}^{-2}\)). Receiver D had the least bulky dataset for this evaluation and good results of its error indicators. Its largest deviations ranging from 0.22 m to 0.26 m in the number of 50 samples and also occurred at higher speeds (specifically, at speeds of 6.6-6.8 m s\({}^{-1}\) and an acceleration of 0.2 m s\({}^{-2}\) to 0.3 m s\({}^{-2}\)). The monitored error indicators \(\mu_{err}\), \(s_{err}\) and \(RMS_{err}\) from the \"FIX\" state of the receiver did not equally reach large values compared to the deviations calculated from all the measurements. Large deviations were the most pronounced for Receiver D, which had the lowest \(SSR\) indicator. It can be concluded that, when the cheap RTK receiver can reach the \"FIX\" state, its measurement achieves a great accuracy, even greater than Receiver A.