Comparison of image georeferencing strategies for agricultural applications of small unoccupied aircraft systems

Abstract

Small unoccupied aircraft systems (sUAS) are becoming popular for mapping applications in agriculture, and photogrammetry software is available for developing orthorectified imagery and three-dimensional surface models. Ground control points (GCPs), which are objects or locations with known geographic coordinates, may be required for accurate image georeferencing. However, few studies have compared global position equipment among sUAS or investigated the effects of GCP number or arrangement on georeferencing accuracy. The objectives of this study were to evaluate numbers and configurations of GCPs for georeferencing sUAS-acquired images and determine the GCP requirements for sUAS with and without real-time kinematic (RTK) global positioning equipment. The effects of varying numbers and configurations of GCPs were investigated on both a 0.40-ha area the size of a typical plant breeding trial and a 64.7-ha area (i.e., a U.S. quarter section) the size of a typical agricultural production field. Results demonstrated that four GCPs placed at the corners of the breeding-scale field resulted in two-dimensional (2D) error of ±3 cm in the absence of RTK, with minimal improvements when including more GCPs. The orthomosaics from the RTK-equipped sUAS demonstrated improved 2D accuracy even without the use of GCPs, with a maximum mean error of 0.08 m. Four GCPs were found to be sufficient to reduce altitudinal (Z) error, with maximum mean error of only 0.05 and 1.98 m for the RTK and non-RTK flights, respectively, for the production-scale field. Thus, using four GCPs, RTK-equipped sUAS, or a combination will result in improved georeferencing for photogrammetry products.

Yield prediction in a peanut breeding program using remote sensing data and machine learning algorithms

“…Ground control points (GCPs) were collected using two paired Emlid Reach RS2+ (Emlid Tech Korlátolt, Budapest, Hungary) devices, where one device was placed on a fixed, permanent base location and the other was used as a rover to collect the GPS data for each GCP. Because prior research has demonstrated that four accurate and precise GCPs near the corners of each flight mission are sufficient to georeference photogrammetry projects, that is the number that was used in this study ( Pugh et al., 2021 ).…”

Unmanned Aircraft System (UAS) Structure-From-Motion (SfM) for Monitoring the Changed Flow Paths and Wetness in Minerotrophic Peatland Restoration

“…Despite direct georeferencing being possible with the onboard-RTK, the use of some GCPs is recommended for full accuracy. In the case of small square mapping extents, at least four GCPs are recommended [63]. For larger extents, at least one additional GCP is recommended in the central area [64,65].…”

Evaluation of Remotely Piloted Aircraft Systems (RPAS)-based Structure-fromMotion (SfM) photogrammetry for characterizing microtopography and vegetation structure in a southeastern Ontario peatland

“…More specifically, GCPs are often laid out around the perimeter as most distortion occurs in these areas during model construction (Gabrlik, 2015;Sanz-Ablanedo et al, 2018). It is important to note, that having more GCPs that are evenly dispersed increases horizontal and vertical georeferenced accuracy of the spatial data products (DTM/DSM models, orthomosaic images, or point clouds) (Pugh et al, 2021). For example, in the works of Forlani et al, (2019), implementing just one GCP decreased error from 10 cm to 3 cm.…”