# GNSS Signal Quality in Forest Stands for Off-Road Vehicle Navigation
## 3 Results
### GNSS Signal Quality Evaluation  
The evaluation of the quality of the GNSS signal was performed using the GNSS Trimble Geo XR with Zephyr model 2 Geo XR antenna, and the Trimble Geo 7X cm version with antenna Tornado for 7X devices--see Section 2.2 Measurement Methodology for more details. The files recorded by the receiver were used for the evaluation (analysis) of satellite signals. The recorded binary files of type *.SSF from area 1 were transferred to text format by the SSF Editor application, which is part of the PathFinder Office program. A sample of part of the content of the records taken during the measurement in area 1 is shown in Figure 8.  
The following information was obtained and evaluated from the text files:  
* Number of satellites of individual GNSS types;
* GNSS receiver antenna coordinates in 1 s intervals;
* Accuracy estimates (standard deviations) of coordinates in the direction \"north-south\"--sigma north \((\sigma_{N})\), \"east-west\"--sigma east \((\sigma_{E})\), and height--sigma up;
* Average values of PDOP and SNR of satellite signals during measurement;
* GPS connection time to all records. A specific example of one measurement record (no. 582) related to GPS time (25.8. 2020, 8:03:10,000) is shown in Figure 9.  
The number of individual GNSS satellites from which data was received during vehicle movement measurement in area 1 is shown in Figure 10.  
Figure 10 shows that the largest number of GNSS satellites in area 1 belonged to GPS (9-11), followed by GLONASS (7-9). In the case of Galileo or BeiDou, the number of satellites were rather marginal. Figure 11 shows that the largest number of GNSS satellites in area 2 belonged to GPS (6-9), followed by GLONASS (4-6), Galileo (2-4), and BeiDou (0-6). It can be assumed that currently the number of correresponding satellites will be much more favorable. It is worth noting that all positioning was performed in autonomous mode. derived from data contained in *.SSF files from area 1, \(\sigma_{Hz}=\sqrt{\sigma_{E}^{2}+\sigma_{N}^{2}}\), where \(\sigma_{E}\) is the estimate of accuracy in the \"east-west\" direction and \(\sigma_{N}\) is the estimate in the \"north-south\" direction--see also detail in Figure 14. The red squares show the position deviations, \(d_{Hz}\), detected as the difference between the position recorded by the GNSS receiver and the position determined terrestrially. The terrestrially determined positions (coordinates) were assumed as reference data due to the assumed accuracy of the GNSS measurement results. These route reference points (along which the vehicle drove) were measured terrestrially using tachymetry and signaled on the terrain surface (spray on the ground). Vehicle movement time on the route was displayed in hundredths of seconds. Note that the positional (horizontal) deviation \((\sigma_{Hz})\) was calculated according to the formula \(d_{Hz}=d_{t}\sqrt{2}\), where \(d_{t}\) is the distance of the GNSS determined position from the reference route (Figure 14). It was clear that the positional accuracy \(\sigma_{Hz}\) was very pessimistic, \(\sigma_{Hz}>d_{Hz}\) was almost exclusively valid. The size of the actual positional deviations from the route was approximately \(2\times\) to \(4\times\) smaller. However, a general statement could not be made from the described fact. The statistical set was from a small scale of space and time. An overview of the reliability of the data of the horizontal error \(d_{Hz}\) with respect to the actual course of the vehicle route can be made using Figures 15 and 16. In Figure 15, the projected (planned, terrestrially focused) route of the vehicle is shown by line segments. Blue triangles show the position of the vehicle determined by GNSS measurement. It should be noted that the GNSS position shows the movement of the vehicle including its approach to the projected route. In Figure 16, circles show the horizontal errors, \(\sigma_{Hz}\), which are contained in *.SSF files (see Figure 8).