In 1999, prototype self-steering ag equipment could get the angle of the working implement (bulldozer blade) by having GPS antennae on the perimeter of the vehicle. The lack of OpenCV and such made full-automation imposisble without a driver in the cab at the time. But, a collision avoidance system that could handle autonomous AND piloted rigs together was already in an advanced prototype stage ( basically, an automated "aircraft" controller that would say to the driver "wait", "accelerate" or "turn")

Backgrounder on GPS tech at the time: accuracy was ~10 mm in the horizontal, ~1 m in the vertical when differential GPS was used. Differential GPS means a well-known, fixed base station (WAAS or your own) provides error-correcting deltas over a packet radio link. (This would also eliminate any SA injected error, so SA was pointless to all but stand-alone receivers.) TRMB's differential GPS was called "kinematic" because the differential calculations would be valid while receivers were in motion, whereas most others at the time would only be sufficiently accurate when base and receivers were stationary. Their receivers were extra accurate because of the, at the time, expensive pseudo-wavelength + relativistic measuring of the receiver-satellite distance.

With tech advances and scale, it makes sense that such tech becomes widely available.

(TRMB's founders designed GPS)