How is speed calculated? (Nuvi 660)

When I select the speed display on my Garmin GPS, how can I know the
accuracy?

I understand that most accurate speed is calculated via doppler shift
measurement from satellite signals.

The lesser-accurate way to calculate is simply by the change in distance over
time.

Which speed calculation method is used in the Nuvi 660?

Thanks,
Dave

Doppler, from the PVT solution.
=20
--=20
Alan White
Mozilla Firefox and Forte Agent.
By Loch Long, twenty-eight miles NW of Glasgow, Scotland.
Webcam and weather:- http://windycroft.co.uk/weather

Op 10-2-2011 14:48, DaveC schreef:
no doppler, just distance and time. You can see that on some GPS models
if you leave it on the table it 'walks' around and indicates a speed
because its coordinates change in time.

Doppler, from the PVT solution.
-
Alan White

-=-=-=-

-
t. chabot

-=-=-=-

I just *love* USENET! Ask a question, choose an answer! ;-)

Yes, I see that sitting still after powering on the Garmin 660, the speed
display jumps as much as 1.5 MPH.

So it looks to be coordinate delta calculation.

How accurate is such a speed calculation?

Thanks,
Dave

The "Doppler" answer pops up briefly when this question gets asked,
but it seems to have no basis in fact and fades quickly. I wouldn't
choose it as the answer. :)


Pretty darn good when underway because the errors cancel each other
out and what's left gets averaged.