Several brands of equipment have been used with global positioning systems (GPS) in Precision Agriculture. The quality of these different receivers varies according to their capabilities in terms of accuracy and repeatability. In this study, three commercial systems were tested to compare their accuracies. This study focused on measuring the stability of the receiver and the repeatability of data. The study was conducted in the experimental area of ESALQ/USP. It consisted of three parallel 50-meter lines spaced 10 meters apart. Data collection was done on 9-25-2002 with a total of six replications. Data was collected simultaneously and the date and time of data collection were chosen to minimize the physical dilution of precision (PDOP). The three receivers had quite different performance. The GPS "A" (8-channel) had the highest variability and the lowest repeatability of data. The differential GPS (DGPS) "B" (12-channel) had higher accuracy, with a maximum deviation of 6m, but with significant repeatability. The GPS "C" with optimized algorithm had the highest accuracy and deviations no greater than 2m. Both GPS's "B" and "C" are adequate for Precision Agriculture uses.
precision agriculture; GPS; positioning accuracy
