Barry Gershenfeld <barry_g@ZMICRO.COM> wrote:
> > Does the error of a standard GPS receiver affect it's ability to determine
> > a vehicle's or vessel's speed accurately, or is it safe to assume that the
> > error will be constant and the speed it reports will be accurate?
>
> "Error of a ...receiver" implies that you're talking about transmission
> path and receiver noise effects.

Not necessarily. The errors could arise from receiver clock errors and
geometric dilution of precision (GDOP).

> These receivers use the doppler shift of the signal to determine speed
> and direction, so it's not connected to position.

No, GPS receivers don't use Doppler to determine receiver motion; the
velocity of the transmitters (satellites) is typically 2 orders of
magnitude greater than that of the receiver.

> Even in the bad old days of Selective Availability, speed and direction
> were more accurate than position.

Mainly because the "frequency spectrum" of the SA noise is well below the
frequencies associated with vehicular motion; if you're on foot, however,
the effects are quite noticable.

-- Dave Tweed

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