100KM

GPS ground speed 2D or 3D ?

Does anyone know if gps ground speed data is purely 2D or can it compensate for changes in altitude ?ie... if a plane was flying in still air and it was in a 45 deg dive @ 30 knots airspeed , would the gps speed register 15 knots or 30?

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  • GPS speed (and heading) are calculated from taking sequential recordings of the location (lat and long) and comparing them. Since lat and long are 2D, it follows that speed (and heading) are also 2D.
  • Moderator
    Ah well, perhaps better to think of it as groundspeed I think.

    So the wind would be more of a factor, ie if its into it or not. 30 knot airspeed into 15 knot wind 15 knots over the ground, turn that around and head the other way you would still be fly at 30 knots but making 45 over the ground.

    I think I would be right in saying the only way to measure the airspeed of the airframe would be with a pitot.

    Oh I see where you are going with that now I have re-read it.

    I think it would adjust, otherwise how else can it stay looking right when I'm flying a real aircraft??

    But I stand to be corrected, a better explaination will be forthcoming I'm sure!

    G
  • 3D Robotics
    That's a good question. I'm thinking 15 (ie, GPS ignores altitude when calculating ground speed) but have never tested that.
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