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Stanley “Jay” Solomon, Jr.
Low-cost GPS for Agricultural Applications
University of Illinois faculty and extension educators have conducted research/demonstration projects on the capabilities and accuracy of consumer grade hand-held GPS receivers and pocket PC's for on-farm applications.
Several consumer-grade GPS receivers were evaluated for accuracy and precision with respect to potential onfarm applications. Accuracy is a measure of a receiver's ability to average to the correct location. Precision is a measure of a receiver's ability to consistently repeat its location, which may or may not be the correct location (see figure 1). The static test results indicate the receivers are within 4.5 m (15 ft) of a known location 95% of the time (table 1). Four receivers were less than 2.8 m (9.2 ft) from the known location 95% of the time. The dynamic test demonstrated the ability of all the receivers to provide useful path and area data. The boundaries collected over-laid each other with minor visible variation. All the receivers recorded areas within 0.004 ha (0.07 ac) of the 0.71 ha (1.75 ac) test area calculated from the Trimble AgGPS 122 receiver data. The GPS receivers evaluated were a cross section of those commercially available for less than $300.
Based on initial results, several on-farm projects have been initiated including: yield mapping, grid soil sampling, crop scouting, and as-applied manure mapping. Approximately 400 acres were harvested using the low cost receiver. Grid soil sampling and crop scouting systems utilized laptop or hand-held PC's. The as-applied mapping system was installed on a pork producer's manure application equipment and tested with water application during the summer of 2004. The system successfully recorded the travel path of the equipment, geo-referenced flow rate, total fluid applied, and calculated geo-referenced application rate. This system also documented compliance with environmental regulation for protection of water quality.
Circular Error Probability from estimated true location 50% 95% ft ft AgGPS 122 (R) 1.2 AgGPS 122 (R) 2.2 AgGPS 122 (G) 2.6 AgGPS 122 (G) 4.5 Navman 3.4 Navman 7.9 Pocket Xtrack 5.4 MAP330 8.1 Legend 5.7 D157N (S) 9.0 D157N (S) 5.9 Pocket Xtrack 9.1 D157N (F) 6.1 Legend 10.9 Clip-On Bluetooth 6.2 Clip-On Bluetooth 11.9 MAP330 8.1 D157N (F) 14.3