## 2 Materials and Methods  
### Study Area and Harvester Positions Data  
The study was carried out in a southern boreal forest zone in Kolmikanta, Tuusniemi, Finland (62.67\({}^{\circ}\) N, 28.47\({}^{\circ}\) E, 158-162 m above sea level) (Figure 1). The study was carried out within a managed spruce-dominated stand. The average diameter of the trees was 25.2 (\(\pm\)5.86) cm, median 26 cm. The range was 16.5-44.5 cm. The average height was 21.6 (\(\pm\)2.7) m, median 22 m. The range was 16-26 m. The stand underwent mechanized commercial thinning by an eight-wheeled Ponsse Ergo cut to length (CTL) harvester.  
The Trimble R12 GNSS receiver was used to collect multi-constellation GNSS data. Leica Nova T560 robotic total station was used to collect the true positions of the harvester. The Trimble R12 and a prism for total station tracking were installed on the roof of the Ponsse Ergo harvester (Figure 2). The true position of Trimble R12 was calculated by measuring the offset between the prism and Trimble R12. The exact time based on GNSS signals was used to synchronize the measurement time between the total station and the Trimble R12. The Trimble R12 measurements were carried out in RTK mode using the Trimnet network of reference stations available in Finland. The technical characteristics of the Trimble R12 are presented in Table 1. The accuracy numbers in the specifications only apply in open-sky conditions with nothing blocking the satellite signals.  
The specific settings in Trimble R12 were selected to facilitate the data collection. The following details outline the selected settings:  
* Inclination correction was disabled;
* Position was measured at a frequency of 1 s;
* The altitude mask was set to 10 degrees;
* The PDOP mask was set to 25.5;
* Horizontal and vertical tolerance were set to 99,999.9, which essentially disabled these parameters;
* The R12 device incorporates a feature called \"xFill\", which attempts to obtain RTK correction via a satellite data link if it cannot be obtained through 2G/3G.  
Figure 1: Map of the study area and established test plot with measured harvester positions. Background: unmanned aerial vehicle (UAV) and red, green, blue (RGB) image mosaic.  
Figure 2: The Ponsse Ergo harvester and the equipment installation on its roof: the Trimble R12 (a); the prism (b).  
The harvester's real positions were measured by a total station with a frequency ranging from 1 to 5 measurements per second. The Trimble R12 GNSS receiver's positions were measured with a frequency of 1 Hz. To combine the positions from the total station to the Trimble R12 GNSS receiver, the positions from the total station were averaged into 1 s intervals. Total station observations deviating more than 8 mm within 1 s interval were excluded to guarantee that averaging would not introduce an additional error to the analysis. GPS time was used to synchronize the total station and the Trimble R12 observations.  
For each of the Trimble R12 positions, the following additional parameters were recorded: solution type, HDOP, VDOP, PDOP, DOP, total number of satellites and satellites from each constellation observed, GPS, and GLONAS. To calculate the absolute deviation for each GNSS position relative to the total station, the easting and northing coordinates of the total station were subtracted from the corresponding GNSS position. According to the Trimble R12 specification (Table 1), the RTK accuracy is 8 mm horizontal and 15 mm vertical. Based on this, the prism points with a deviation of more than 8 mm in an east or north position were classified as inaccurate points.