[FOSS-GPS] Why Gamin 18X is too precise?

Brian Wilson brian at wildsong.biz
Tue Apr 7 10:45:51 PDT 2015

GPS uses Doppler to measure velocity. See
 and especially the comment that Garmin really is probably accurate to .5
not .1 miles per hour (or roughly knots)

In the 18X spec sheet I see this Accuracy
> • GPS Standard Positioning Service (SPS) Position:
> < 15 meters, 95% typical
> Velocity: 0.1 knot RMS steady state
> • WAAS
> Position:< 3 meters, 95% typical
> Velocity: 0.1 knot RMS steady state

Maybe you are reading the wrong section? I don't see any reference to .05 m
/ s

Also note that "RMS steady state" implles they are doing averaging.

Hope this helps


On Tue, Apr 7, 2015 at 1:31 AM, solver90 <salimzairmilk at hotmail.fr> wrote:

> I have a Gamin 18X to do some experiment with it in urban area
> when i saw the manual
> (http://static.garmincdn.com/pumac/GPS_18x_Tech_Specs.pdf), this GPS has
> an
> accuracy in position of 5m in RMS, and an accuracy in velocity of 0.05m/s.
> My question is: How can we have this accuracy in term of velocity?
> (additional sensor inside the receiver, other signal used,....).
> Thanks
> --
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Brian Wilson, GISP
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