## 1 Introduction
This opens the possibility to develop complex GNSS systems consisting of several GNSS receivers using ROS. The combination of multiple GNSS receivers allows for more efficient determination of position, azimuth, velocity and tilt. The benefits are particularly evident when measuring moving objects. Consistency assessments of GNSS satellite measurements and conventional track tacheometric measurements are covered in [8]. The authors present the results of a comparative analysis of measurements made on a selected test section characterized by rather unfavorable conditions for both tacheometric and GNSS measurements. The tacheometric method was found to be more accurate than the kinematic GNSS method for determining the track axis. The agreement between the two methods was within a standard deviation of 10 mm. Optimal GNSS data acquisition frequencies were recommended for specific speeds of the measurement vehicles. Ensuring availability and reliability of positioning, especially in places with limited access to satellite signal (in tunnels, in areas with dense concentration of buildings and in forest areas), was solved by combining GNSS and inertial system with RTK receiver support and the Ekinox2-U system was developed [9]. The Ekinox2-U system can meet the positioning accuracy requirements for rapid inventory of existing rails up to 3 cm (\(p\) = 0.95), as well as design and construction works with the required accuracy up to 10 cm (\(p\) = 0.95). On the other hand, the system cannot be used to determine the location and extent of track deformation with the required accuracy of up to 1 cm (\(p\) = 0.95). The use of a special KRAB trolley for continuous monitoring and analysis of the quality of the track geometry in the transition zone is discussed in [10]. In transition zones, where different construction materials interact, deformations occur and need to be monitored. The absolute position on the track was determined by a GNSS sensor mounted on the KRAB device, and a precise relative measurement based on the short-fixed chord principle was performed by the KRAB device. The measurements were linked to a precise geodetic network built along the line. Optimization of GNSS measurement method selection using geospatial data and Geographic Information System (GIS) tools was discussed in [11]. The principle of the solution was based on segmenting the area of interest and using spatial analysis to assign the most appropriate GNSS measurement method (static, RTK, DGNSS, etc.) to the segment. The analysis is performed on datasets of orthophotos, topographic maps, digital elevation models, digital surface models (natural and built environment), mobile operator signal coverage data and the location of permanent GNSS station availability. The use of GNSS technology for condition monitoring of bridge structures is discussed in [12]. The solution principle is based on the implementation of a probabilistic approach and is demonstrated by evaluating a bridge in-service. The GNSS measurements were repeated three times during a week under different daytime conditions. Based on the data obtained, a comprehensive probabilistic study was developed based on dynamic displacements in terms of reliability index and probability of failure. An optimized technological procedure for precise determination of the absolute position of points of the geodetic network along the railway line, with an accuracy of 10 to 15 mm, using GNSS for use in railway construction during construction and maintenance of the railway line and its spatial position has been published, for example, in [13]. The terrestrial measurement of the spatial position of the track follows the geodetic points determined in this way. Based on pilot measurements, the technological procedure was introduced into the operating rules of the Railway Administration, State Organization. The subject of this article is the presentation of the results of experimental research aimed at answering these questions:  
1.