On the History Channel they show tractors being guided by GPS. At the beginning and end of the first pass POIs are recorded. Then each subsequent pass is determined by the width of the implement. John Deere claims each pass is accurate to less than 2 inches. How does that work?
It's what is known as Differential GPS or DGPS. A signal from a terrestrial location is broadcast and the two signals are compared at the receiver. The differences tell the unit how far it needs to move in order to be at the exact point. The Gov. system yields differences of less than 1 cm, but it takes two receivers. One for the sat signal, one for the correction signal and a fairly powerful processor to calculate the differences. It's often used for surveys.
raven makes one for farming - you might try their site to see if they have add'l information.
John Deere has many links to articles, if you search their website for 'gps'
Here are a couple:
Thanks for the replies. A friend that visits this site sent me an email. He said his neighbor has the premium service from John Deere. Two years ago, his display showed that he had one more "round" with the combine when in fact he had finished. So he backed up the combine to see if the display would update. He backed into his pickup truck.
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