http://www.stormcam.org/auto-gps/
How does GPS auto steer work??
Hi there, can you please help me, I need to know as much as I can about GPS auto steer in agriculture.
Why?
How?
Set up/equipment required?
Providers?
Ongoing costs?
everything you can help me with please!!!!
Thanks in advance 
Why- Accuracy, driver fatigue, fuel, seed, fertilizer, chemical savings.
How-The first answerer gave a good explanation of how GPS works. A GPS receiver is connected to the tractor/combine/applicator’s steering hydraulics and controls the steering. How much money you want to spend determines the accuracy. Most standard auto-steer systems are sub meter, but for enough investment you can get down to sub inch accuracy (this requires ground stations in addition to satelites).
Equipment required-Gps Antenna, receiver, steering control box and instructions.
Providers- Outback, John Deere (Greenstar), Auto Farm, Trimble, Raven. That’s not all but it’s a list of the ones that have been around longest.
Cost-The higher end autosteer (sub inch accuracy) can run $50,000 +. Outback is a good sub meter system and you can get into it for under $6,000. If you subscribe to a service, there is a yearly subscription cost to get connected to the satelites, or you can use a free one (WAAS is one I use).
GARMIN NUVI 265WT vs. Mio Moov 200 AUTO GPS ROAD TEST REVIEW OF GARMIN