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.
Hmm, so are they using laser transits as the input to adjust implement height when leveling fields? I always assumed it was dGPS, but 1m in the vertical isn't nearly enough.
Robots have been (helping) grow our food for quite a while now and we just don't think of it that way.
RTK GPS is quite common for levelling applications. It's closer to 25mm in the vertical when a local (~10km) base station is used. Lasers are used but have line-of-sight and atmospheric distortion issues.
Yes, lasers. Even with the higher accuracy and more expensive real time dGPS systems the vertical accuracy isn't as good as horizontal. When you're looking for a very shallow gradient in a field for irrigation GPS just isn't as good as a laser level.
Much of the problem is geometry, while you're likely to have a good spread of satellites around your receiver horizontally they're all on one side of the vertical solution your receiver is calculating.
3 sats are needed for a two point fix, 4 for a one point fix, and 5+ help with accuracy if they're not clumped near each other (the constellation's always moving). At higher altitudes such as in a plane at FL 350 with sats below the receiver, vertical accuracy increases some compared to ground, which makes these obvious: http://www.gps.gov/applications/space/
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)