## 3 Results  
The position coordinates recorded by the geodetic GNSS receiver, i.e., the latitude and longitude, were provided in an angular (curvilinear) measurement, preventing the direct determination of the XTE value in metres, in relation to the designed sounding profiles. For this reason, the geographic (angular) coordinates were projected from the surface of the World Geodetic System 1984 (WGS84) ellipsoid (with the parameters of a = 6,378,137.00 m, b = 6,356,752.314) [32] onto a flat surface using the Gauss-Kruger transformation commonly applied in geodesy [33]. The calculations yielded two-dimensional coordinates (x, y), where the x value represents the distance (in metres) between the point and the equator, calculated along the meridian arc (on the WGS84 ellipsoid), and the variable y is the distance (in metres) to the arbitrarily set central meridian. The minus sign indicates that the point is located to the west of the meridian, while the plus sign corresponds to a location to the east of the meridian. In order to avoid negative values of the coordinates on the y axis, a constant value of, for example, 500,000 m (each zone in the PL-2000 system spanned 3\({}^{\circ}\) of longitude) was frequently added to the result [34; 35]. The studies used the PL-2000 system, and the replacement of angular coordinates into Cartesian coordinates was conducted based on the following mathematical relationships [36]:  
\[ \begin{array}{ll}x=m_{0}\cdot N\cdot&\left[\frac{S(B)}{N}+\frac{(\Delta L)^{2 }}{2}\cdot\sin(B)\cdot\cos(B)+\frac{(\Delta L)^{4}}{24}\cdot\sin(B)\cdot\cos^{ 3}(B)\cdot(5-t^{2}+9\cdot\eta^{2}+4\cdot\eta^{4})+\right.\\ &+\left.\frac{(\Delta L)^{6}}{720}\cdot\sin(B)\cdot\cos^{5}(B)\cdot(61-58\cdot t ^{2}+t^{4}+270\cdot\eta^{2}-330\cdot\eta^{2}\cdot t^{2}+445\cdot\eta^{4} \right]\end{array}  \tag{1}\]  
\[ \begin{array}{ll}y=m_{0}\cdot N\cdot&\left[\Delta L\cdot\cos(B)+\frac{( \Delta L)^{3}}{6}\cdot\cos^{3}(B)\cdot(1-t^{2}+\eta^{2})+\right.\\ &+\left.\frac{(\Delta L)^{5}}{120}\cdot\cos^{5}(B)\cdot\left(5-18\cdot t^{2}+t^ {4}+14\cdot\eta^{2}-58\cdot\eta^{2}\cdot t^{2}+13\cdot\eta\right)\right]\\ &\left.+5000000+\frac{t_{0}}{3}\cdot 1000000\end{array}  \tag{2}\]  
Figure 8: The window of the u-center software used to save messages recorded by the navigation multi-GNSS receiver in the National Marine Electronics Association (NMEA) standard. where \(m_{0}\) is the scale factor (-), \(N\) is the ellipsoid normal (radius of curvature perpendicular to the meridian) (m), \(S(B)\) is the meridian arc length from the equator to the arbitrary latitude (B) (m), \(\Delta L\) is the distance between the point and the central meridian (rad), \(B\) and \(L\) are the ellipsoidal coordinates of the point (\({}^{\circ}\)), and \(L_{0}\) is the longitude of the central meridian (\({}^{\circ}\)). The other parameters of projection to the two-dimensional Cartesian coordinates in the PL-2000 system include:  
\[t=\tan(B), \tag{3}\]  
\[\eta=\sqrt{\frac{e^{2}\cdot\cos^{2}(B)}{1-e^{2}}}, \tag{4}\]  
where \(e\) is the first eccentricity (-). Then, in order to determine the XTE distances, it was necessary to describe each route profile in a mathematical manner.