You sure? Satloc was doing GPS guidance for aerial guidance for decades (crop dusting planes). They adapted it for ag guidance in the 1990s I believe. This technology has been evolving for years and saying that John Deere or some single company invented it sounds like a gross oversimplification.
> The Beeline Navigator was developed in 1993 by Australian engineer, Rob Mailer. [1]
[1] http://www.queenslandcountrylife.com.au/news/agriculture/mac...