## 4 Discussion  
This study presented a low-cost method of GNSS positioning accuracy assessment for agricultural machinery, based on the commonly used GNSS corrections in Croatia. Its properties of straightforwardness and adaptability under various conditions in the study area meet the requirements of a potential basis for widespread global application [36]. Unlike available ISO standards for the evaluation of GNSS RTK receivers [17], it simulates the actual movement of the agricultural machinery during the agrotechnical operations, which has more practical importance for the farmers in their work. The majority of technological improvements and applications in precision agriculture are still largely focused on GNSS positioning and navigation, as the basis of all precise agrotechnical operations [37]. Its importance is described in many previous studies and its importance is expected to grow further [38]. Despite its availability and mentioned advantages, the proposed method at the current stage still has two main drawbacks:  
* The retained minor subjective impact of the operator on the GNSS positioning accuracy;
* The lack of newly available GNSS corrections and multiple study areas. The first disadvantage of the operator's subjective impact on the reliability of GNSS observations occurs due to the imperfections regarding steering aim and reaction time [39]. The selection of EZ-steer justifies the selection of two repetitions due to assisted guidance and removal of the vast majority of steering subjective errors caused by the operator. This solution is cost-efficient but not perfectly reliable, which could be resolved with the more expensive use of an autosteering solution in future studies. Additionally, the fewer repetitions are user-friendly to farmers, being time-efficient regarding fieldwork and data processing, allowing the widespread and efficient implementation of the proposed method. However, more repetitions would produce more reliable results and farmers who prioritize additional accuracy over time efficiency should opt for more than two repetitions. These errors have a random character and a previous study indicated that these can be minimized in the process of statistical analysis [40]. The minor subjective assessment of the operator remains a disadvantage of the proposed method but ensures a time-efficient and low-cost property, which can be a priority to farmers. The proposed method is applicable with the autosteering solution, as [PERSON] et al. [8] noted the maximum retention of positioning accuracy by applied GNSS correction but also its practical constraints, because of which it might not be available to a wide range of farmers. As another more expensive option, the possible upgrade of this method is the implementation of an automated procedure, simultaneously using two GNSS receivers mounted on the agricultural machinery. One GNSS receiver with maximum available accuracy GNSS RTK corrections could be used for an actual reference positioning, which corresponds to CROPOS in this study. The second receiver with GNSS corrections, which are evaluated in the process, coupled with autosteering to remove the effect of human error, could round up an upgraded version of the proposed method. Since the positioning accuracy of the reference receiver equals 2 cm horizontally [7], this approach will be optimal for the assessment of the performance of corrections up to 10 cm, such as SBAS. This approach does not require setting up a projected trajectory, which makes it even more flexible for widespread application. However, this is not a low-cost method and is time-expensive due to the necessity of coupling two GNSS receivers in the same agricultural machinery [41]. While this study covered the most commonly used GNSS corrections for farming purposes in Croatia, the second disadvantage is based on the current lack of testing of the reliability of the proposed method using the additional corrections and study areas.