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9171RE: [tracker2] How to deal with GPS drift with OT2?

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  • Fred Hillhouse
    Nov 2, 2009
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      I got a brand new GlobalSat BR-355 SiRF GPS which I use on
      the secondary port of the OT2. Unfortunately, I discovered
      that the position is drifting severely when the car is parked
      for several hours at the same place (covered or uncovered),
      sometimes up to 300ft. This may be due to reflections.
       
      This is a common. The satellites are always moving in the constellation. I wonder if your receiver is more sensitive than mine. Or does mine have more filtering to keep from ping-ponging me around. Covered is usually not a good place place to park for a GPS, especially if it is a metal cover. Any signal it receives will be either from low on the horizon or reflecting from some other surface. Judging by the overhead view, your view to the horizon is blocked.
       
      I tried with WAAS enabled and disabled, 
       
      This will only matter if you can actually see the WAAS satellites. They are geo-stationary which means they are lower in the sky (New England anyway). Building, trees will attenuate then quite a bit. BTW, with software packages like Orbitron you can see where in the sky the WAAS satellites are as well as the regular constellation.
       
      I found this to be an interesting and educational read.
       
       
      and with Static Navigation enabled and disabled and get the
      same problem. Static Navigation is supposed to fix this by
      correcting the coordinates if the calculated position moves
      slower than 1.6 m/s. It does not work: calculated moves
      are grater than that. 
       
      If the GPS is turned off then the last valid location will be remembered as used. However, turning the GPS off means that there is a delay until the unit reacquires. A relay breaking the GPS TX line to the T2 might serve well. I have not tried that but it may work for you.

      I contacted the manufacturer and they said
      the best option is to have the software deal with it. 
       
      That is true in regards to their GPS. Some units do some filtering, some do none. Yours apparently does none and may be more sensitive as well.

      Does anybody sees how to eliminate drift in the OT2?
       
      I saw other answers like increasing your slow speed. That is a good direction to try.
       
       
      Best regards,
      Fred
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