# GNSS Signal Quality in Forest Stands for Off-Road Vehicle Navigation
## 5 Conclusions  
The aim of this study was to investigate the accuracy of off-road vehicle navigation using GNSS receivers in typical forest stands of the temperate climate zone of Central Europe. For this purpose, two localities were chosen in which reference elements (trees and vehicle routes) were precisely located by tachymetry, which were then combined to determine the accuracy of the moving vehicle. Positioning accuracy (\(\sigma_{\rm HZ}\)) and position deviations (\(d_{\rm HZ}\)) detected as the difference between the position recorded by the GNSS receiver and the position determined terrestrially, were determined.  
The introduced research studies prove that GNSS navigation devices can be successfully used for approximate localization of moving vehicles, especially when it comes to movement in a sparse forest. Bigger problems will arise if we seek to accurately determine vehicle-tree collisions while maneuvering the vehicle between trees. In this case, it will be necessary to install terrestrial laser or radar sensors of tree positions and calculate the vehicle's route in real time. However, this type of navigation has limited possibilities given the cover of trees and the fact that trees cannot be mapped beyond the horizon. Therefore, support using remote sensing means will also be necessary, or support using autonomous navigation, based on measuring acceleration, or determining the position using an odometer and gyroscope.  
Additionally, an unscented Kalman filter (UKF)-based multi-sensor optimal data fusion methodology for INS/GNSS/CNS (inertial navigation system/global navigation satellite system/celestial navigation system) integration based on a nonlinear system model can significantly improve navigation options in terrain covered with vegetation and can provide a reliable positioning solution in case of GNSS (GPS) blockage--see [37; 38; 39]. In addition, the methods based on the fundamental improvement of the fusion mechanism using matrix weighted fusion can significantly improve the quality of determining navigation in vegetation in the future--see [42; 43].  
The GNSS measurement issue under poor environments can also be addressed by identification of abnormal measurements. Some methods have been proposed to optimize off-road vehicle navigation deficiencies caused by these abnormal measurements using, e.g., a novel robust fault-tolerant federated filter based on a strapdown inertial navigation system (SINS) [37; 44], global navigation satellite system (GNSS), celestial navigation system (CNS), and doppler velocity log (DVL) [40].  
Organization, M.R.; conceptualization and methodology, M.R. and V.K.; measurement, V.K., F.D., M.R., J.N., P.S. and D.K.; validation, M.R., R.G., V.K. and F.D.; writing the paper M.R., V.K.; original draft preparation, M.R. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Data Availability Statement: Map materials were prepared using mapy.cz application, orthophoto maps using [[https://ags.cuzk.cz/geoprohlizec/](https://ags.cuzk.cz/geoprohlizec/)]([https://ags.cuzk.cz/geoprohlizec/](https://ags.cuzk.cz/geoprohlizec/)), accessed on 10 May 2023, other data were measured and analyzed by the authors of this article.  
This paper is a particular result of the defense research project DZRO VAROPS managed by the University of Defence in Brno, the NATO--STO Support Project CZE-AVT-2019 and the specific research project 2021-2023 at Department K-210 managed by the University of Defence, Brno.  
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.