GPS Speed Calculation

I notice that the vehicle speed calculation appears to be extremely
accurate. Is the Garmin able to obtain this accuracy from the GPS
position estimates considering that they may be noisy and have a time
varying clock drift?

Or does the device somehow make use of Doppler information obtained from
satellite transmissions?

Thanks,
Harvey

Well, after further thinking, it's not likely that Doppler could be used
since it would only yield speed along the vehicle-satellite line of
sight. I guess then that the position data is accurate enough to yield a
smoothed velocity estimate.

Harvey Gratt wrote:

Harvey,

On Sat, 26 Dec 2009 20:56:32 -0600, Harvey Gratt wrote:


You will at some time figure there is a (one off) significant position
error in the log of your trips. ususally that comes when you enter a
region with poor reception (such as a house) and just sit still in
there. With that you will see the maximum speed being _very_ high,
just good enough to go from that sigle one off point to the real
position. Calculate speed for that position error yourself... you will
figure a pretty good match to the reading on the unit.

In my mind, that can only be by the device doing the same calculation
as you did. I do not see why the doppler speed measurement would
always lead to that same result since that would mean that all (at
least 4) doppler shifts are measured incorrect along the same vector!
--

Ciao,
Holger (GUS-KOTAL, GUS#1100, GRR#51)

90-92 Honda CB400 10 Mm | 93-95 Yamaha TDM 850 26 Mm
95-97 KTM 620 LC4 13 Mm | seit 97 BMW R1100GS 69 Mm (Die Renndrecksau!)

cu @ http://www.issle.de

According to my GPSmap 60CSx I once rode Mach 2.5 on my bicycle....

Most of the time, however my Garmin speed is VERY accurate.

On Sun, 27 Dec 2009 06:26:40 -0800 (PST), "H@n Zijsp@n" wrote:


Cool, what type of bike is that? ;-)
IF you still have a log of that trip, I bet the position logged is WAY
off where you really were.
--

Ciao,
Holger (GUS-KOTAL, GUS#1100, GRR#51)

90-92 Honda CB400 10 Mm | 93-95 Yamaha TDM 850 26 Mm
95-97 KTM 620 LC4 13 Mm | seit 97 BMW R1100GS 69 Mm (Die Renndrecksau!)

cu @ http://www.issle.de