Vulnerability of GPS to Provide Vehicle States in Real Time

The essential technology to take emergent applications, such as precision agriculture and robotics, to actual farming fields is readily available and generally accessible. However, the implementation rate of new technologies has slowed down in recent years and remains low at present. An important cause for this negative outcome is given by the lack of long-term reliability found in global positioning systems. This article analyzes the effects of position errors induced by undetected outliers included in the trajectories of vehicles, exposes the major challenges in the estimation of real-time heading and forward speed, and proposes some practical solutions to strengthen the measurement of vehicle states with global positioning devices. In particular, it is recommendable to move beyond embedded quality indicators by implementing strong filtering routines directly on strategic fields of GGA strings. Dynamic states heading and speed greatly benefit from the efficient combination of VTG-based course and velocity with values directly calculated from a sequence of points determined by GGA geodesic coordinates and time. Finally, whenever a grid-based approach is feasible, the reduction of information offered by a mesh results in more robust field mapping as long as global references are maintained for each cell of the crop map.