# Web Mapping for Farm Management Information Systems: A Review and Australian Orchard Case Study
## 3 Case Study Materials and Methods
### GNSS Survey and Imagery Data  
Site imagery was accessed from Google Earth Pro imagery (at 200 m range, from CNES/Airbus for 2023) [46], Bing [57], ESRI [34], and Queensland imagery [48]. Additionally, an orthoimage was acquired over the Central Queensland site in January 2023 using a UAV. A sub-25 kg multirotor drone equipped with a Sony RGB camera (ILCE-6000) and a 25 mm fixed focal lens was flown at an average height of 110 m altitude, capturing photography with a Ground Sampling Distance (GSD) of about 1.6 cm. Ground Control Points (GCPs) were positioned between the orchard rows at approximately 200 m apart (\(n=66\) GCPs over 34.5 ha). The GCP locations were fixed with an Altus ASP3 GNSS rover operating with base station positioned at points established by a Leica GS14 GNSS receiving real-time kinematic (RTK) corrections from the CORS network (HxGN Smart Net, C.R. Kennedy, Melbourne, Australia [58]), with location data captured using the MGA94 coordinate system. The orthoimage and Digital Elevation Model (DEM) were  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Farm** & **Latitude (°)** & **Longitude (°)** & **Elevation (m)** & **Landscape** & **Survey Date** \\ \hline CQ-1 & 23.025080 & 150.641167 & 50–81 & Hilly & 24 March 2022 \\ FNQ-1 & 17.131778 & 145.303059 & 499–521 & Plain & 10 November 2023 \\ FNQ-2 & 17.112235 & 145.100360 & 459–501 & Plain & 10 November 2023 \\ FNQ-3 & 17.134072 & 145.427091 & 587–591 & Plain & 10 November 2023 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Site locations (WGS84) in Central Queensland (CQ) and Far North Queensland (FNQ), Australia, with site descriptors and date of the survey.  
generated in Agisoft Metashape (version 1.5.2.7838), providing two- and five-centimeter GSDs, respectively.  
A minimum of two checkpoints (ground control) were assessed for each site. These points were chosen as being identifiable in Google Earth Pro imagery and ground verifiable. Coordinates were extracted for points at the intersection of two lines, e.g., the corner of a roof or concrete slab. Line segments were extracted from the image using a line segment detector algorithm deployed in OpenCV [59]. The same process was followed for ESRI, Bing, and Queensland web imageries, for historic GE imagery, and for drone imagery. The historical imagery differed in spatial resolution and source; it was from either Maxar Technologies, CNES, or Airbus.  
Field GNSS survey data were captured in WGS84 (GDA2020 epoch) using a GS14 receiver-operated RTK mode through connection to a CORS network for the Central Queensland sites. For Far North Queensland sites, Queensland Government [60] survey control markers (SCMs) close to each farm were located using the application 'Benchmrk' [61] and used as ground control points (GCPs) in the transfer of coordinates to the checkpoints.  
The difference between GNSS and web imagery coordinates of the checkpoints was calculated for eastings (\(\Delta E\)) and northings (\(\Delta N\)) (Equations (1) and (2)) and used in the calculation of a horizontal positional misfit vector (Equation (3)).  
\[\Delta E =E_{GEI}-E_{GNSS} \tag{1}\] \[\Delta N =N_{GEI}-N_{GNSS}\] (2) \[e =\sqrt{\Delta E^{2}+\Delta N^{2}} \tag{3}\]