So it seems like retrofitting for "precision ag" also depends on what commercial "RTK network" is offered in the farmer's local area. I think regular GPS is only ~10 ft accuracy so not sure of farmers are retrofitting tractor steering for that lower resolution.
This has not been true for quite a while. The equipment used on surveying, farming, and construction equipment is much more accurate thanks to the availability of multiple GNSSs (e.g., GPS, GLONASS, Galileo, BeiDou) and terrestrial base stations to remove error (WAAS, DGPS).
Yeah but you don't need commercial services to get down to the inch anymore. Running your own base station has gotten cheap and easy; witness Sparkfun selling their RTK Express kit like hotcakes.
Integrating it into the vehicle is a fun second ROS project for someone who already built a toy robot car. There's a substantial population of highschoolers building the necessary skills, the trick is just to connect them to the jobs.
The kit is the GPS and the steering adaptor that reads the signal. GPS isn't encrypted. The protocol is proprietary, but if you can't reverse engineer it in a day you are a poor engineer. (I wrote the decode for one sub inch GPS, I don't know about our competitors, but I don't see why they would encrypt GPS)
What is encrypted is the steering algorithm to steering controllers. That is about safety, tractors have technically been level 4 self driving for 30 years - not even marketing says that though because the sprit of level 4 self driving is about safety and tractors are just as unready for self driving as any other car on safety grounds. By encrypting the steering control lawyers can ensure the safety warning is displayed. (Sometimes a university is given the encryption keys after legally verifying they won't be unsafe)
Looking again, you seem to be about Rtk. I'm not sure about that. Probably encrypted, but mostly for those who want to charge, you can buy your own base station.
New 'dual-band' GPS systems have 30cm / 1ft accuracy without any basestation requirements. The chips cost $250 instead of $10, and they require different antennas, but 1ft is at a point where dropping further IMO has limited gains.
The highest precision accuracy of RTK devices has vendor-proprietary encrypted signals. E.g: https://www.google.com/search?q=rtk+signal+encrypted+gps+%22...
So it seems like retrofitting for "precision ag" also depends on what commercial "RTK network" is offered in the farmer's local area. I think regular GPS is only ~10 ft accuracy so not sure of farmers are retrofitting tractor steering for that lower resolution.