A tractor guidance system using a differntial GPS (DGPS) is developed to support the driving of a tractor to track the target lines in the field for plowing, sowing, fertilizing, pesticide spraying, harvesting, manuring, grass teddering etc. The system, graphically designed, generate parallel paths automatically according to the work width and displayed more accurate and stable real-time position and direction through a developed filtering method based on Extended Kalman Filter using 3 axis gyroscope with differential GPS, and predicting position and direction after few seconds later considering the delay of the driving operation. The system enables high precise straight and parallel work in the wide field even for a beginner without setting marks. After practiced, the gap from the target line was less than ±20 cm.

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