Accuracy and precision of consumer-grade GPS positioning in an urban green space environment

Abstract

The use of global positioning systems (GPS) has increased in recent years, including for urban forestry management, as a result of its wide range of applications, ease of use and direct use of GPS data in geographic information systems. This study was conducted in an urban green space to assess the accuracy and precision of two consumer-grade GPS receivers with regard to ground control point (GCP) coordinates. Eleven fixed GCPs with known positions were selected and their data collected on four days (two seasons) and three different daytime periods (08:00, 11:00 and 14:00) each day. For each treatment (season and daytime) five replications were recorded. The results showed that the best mean position accuracies were provided by the Colorado receiver in leaf-off period (4–5 m), and its corresponding position accuracies for summer ranged from 9 to 12 m. The results of the Rino receiver mean position error in summer (19–36 m) and winter (10–26 m) were higher than reported in literature. Point averaging had a positive effect on accuracy in both receivers for winter. In summer, three-point averaging was more efficient than five-point averaging. During the day, the Colorado receiver had the best positional accuracy at 08:00 in winter, but in summer there was a large variation in the results. For the Rino receiver there was no general trend; however, results taken at 11:00 and 14:00 were better than those at 08:00. Regarding precision, point averaging had a positive effect on the Colorado while the Rino precision indicated the contrary. The Colorado receiver had better precision than the Rino in both seasons, and was the best in summer. The Rino receiver had better precision in summer compared to winter, and in both recievers daytime had no significant effect on precision. The measured accuracies of Colorado are acceptable for many environment and urban forestry measurement applications and satisfy mapping requirements, but the Rino receiver showed poorer results.