In the last two years, the satellite navigation system GPS has moved to the centre of attention for agricultural applications, especially in the area of guidance systems. Dependent on the working width of the attached implement, these guidance systems can guide the tractor parallel to a defined reference line. This helps the operator avoid overlap or underlap and save costs.
GPS is mainly the single only source of information for guidance systems. This makes the overall system highly susceptible to external influences. Such influences are particularly important in hilly terrain.
The aim of this thesis was to identify main influences and sources of error for guidance systems in order to find possible and suitable solutions. To achieve this, individual error sources have been described and models were developed to minimise these errors. Two basic errors are discussed in detail.
The first error discussed, is the inclination error which is caused by the position of the GPS antenna on the top of the tractor cabin. The second error is the topographical error, caused by the difference between the theoretical plane surface and the real three dimensional and often sloped terrain.
To minimise the inclination error, two inclination sensors were tested on a special test field to compensate the antenna position of the GPS receiver. Because of the measurement technology and the provided accuracy, the two inclination sensors are appropriate for guidance systems and can at least partly replace expensive gyroscopes.
To compensate the topographical error, an algorithm, to correct the error of the slope was developed and tested with real data. According to the situation, the correction of the algorithm was between 0.00 and 114.01 %. In natural occurring situations, a correction of between 84.74 and 114.01 % was calculated.
After extensive research and important insights from the development of the slope-line correction algorithm, both inclination sensors and an optional use of the Z-coordinates in the calculation of guide-lines have been integrated into the optical guidance system "SpurFinder" (developed at the faculty for crop production engineering, TUM). Using Z-coordinates in the calculation of guide-lines' represents an important result of the correction algorithm. Tests with this improved guidance system reconfirmed the suit ability of the two sensors. Also, the theoretical insights could be verified in practice. Through both upgrades, the errors mentioned could be reduced in hilly terrain to an error rate of no more than 20 %.
A commercially available automatic guidance system was also tested. Based on the results of the test runs, concrete suggestions for improvements could be made. Although the system is capable of correcting errors in inclination, it is not capable of detecting and compensating topographical errors.
In the years to come, GPS guidance systems will be increasingly used in agricultural practice. Today, there are already few different systems are on the market, although they still have significant faults regarding their precision, availability and their cost-benefit ratio. Due to constant technology advances, progress in systems and software, these weaknesses are likely to be overcome in the medium-term.
This thesis tries to provide an important contribution, by pointing out the diverse and wide-spread sources of error. It not only offers possible theoretical solutions, but also solutions which have already been set up and tested in practice.
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In the last two years, the satellite navigation system GPS has moved to the centre of attention for agricultural applications, especially in the area of guidance systems. Dependent on the working width of the attached implement, these guidance systems can guide the tractor parallel to a defined reference line. This helps the operator avoid overlap or underlap and save costs.
GPS is mainly the single only source of information for guidance systems. This makes the overall system highly susceptibl...
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