## 1 Introduction  
The advancement of positioning and navigation technology using global navigation satellite systems (GNSSs) ensures its growing use in both precision agriculture and conventional farming [1]. These systems improved multiple aspects of agricultural production since their inception, most notably regarding the accuracy of agrotechnical operations, enabled working hours under lower visibility conditions, as well as lower fatigue for the workers [2]. Moreover, it became a cornerstone of all agrotechnical operations in precision agriculture, allowing precise navigation and implementation of pre-made crop swing, fertilization, and crop protection prescription maps [3]. With Global Positioning System (GPS) and GLONASS fully operational on a global scale, as well as Galileo and Beidou being at the high level of operability, the future of GNSS application in farming will gradually offer more capabilities in the future [4]. The relative observation techniques using GNSS, most notably real-time-kinematic (RTK), provide corrections up to 2 cm for horizontal and up to 4 cm for vertical positioning accuracy [5]. This positioning accuracy ensures high performance for any agrotechnical operation in precision agriculture [6]. In Croatia, this service is provided by the Croatian Positioning Service (CROPOS), distributed nationwide and based on the 33 reference GNSS base stations [7]. However, due to its operating issues near country border areas due to the occasional loss of GPRS connection, as well as the availability of similar commercial positioning solutions, farmers tend to have difficulty in selecting the optimal solution for their needs. Among the present solutions, RTK corrections distributed via radio signal using base stations by individual farmers or local agricultural machinery suppliers are commonly used, as well as the Satellite-based Augmentation Systems (SBASs) data [8]. Among the agrotechnical operations, precision sowing usually demands the highest positioning accuracy [9], while agrotechnical operations, such as fertilization, tend to result in high-performance even with slightly lower positioning accuracy [10]. High requirements for precise positioning were also noted in previous studies for soil tillage and crop harvesting [11]. Therefore, it is mandatory for farmers to know the necessary positioning accuracy per agrotechnical operation and the exact capabilities of available GNSS corrections in their local area for maximum cost efficiency [12]. The latter often highly varies and is subjected to various factors, such as the condition of the GNSS receiver and communication with the base station for transmission of RTK corrections [9], as well as the distance from the base station [13]. Some of these parameters vary within the country or relative location to the base station, so these should be evaluated within the local operating range of farmers. In order to ensure the widespread availability and affordability of this procedure, standardized and low-cost frameworks for GNSS positioning and navigation for agricultural machinery should be developed [14]. Previous studies successfully improved low-cost GNSS hardware solutions [15] and fusion with complementary data sources and methods [16]. However, there is no standardized approach for the accuracy assessment of GNSS positioning for agricultural machinery other than ISO standards, such as ISO 17123-8 for the GNSS RTK field measurement systems [17]. While these standards are useful in some disciplines, such as geodesy [18], they cannot be performed for GNSS receivers mounted on agricultural machinery without their detachment nor do they present actual field conditions during the agrotechnical operations. These standards also do not simulate the real trajectory during agrotechnical operations, containing both straight and curved sections.