4 ms·

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 n

• mojoB 11y ago
  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. This [1] is a good overview of how RTK works. [1] http://www.novatel.com/an-introduction-to-gnss/chapter-4-advanced-gnss-concepts/real-time-kinematic-rtk/ http://www.novatel.com/an-introduction-to-gnss/chapter-4-adv...
• mutagen 11y ago
  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.
  • trimble-alum 11y ago
    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/ http://www.gps.gov/applications/space/