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

[Brian Wilson]

GPS uses Doppler to measure velocity. See
http://gpsinformation.net/main/gpsspeed.htm
 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

1.6.3.4 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


Brian



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
@brian_32768
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