Thread: Which GPS ???
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Old 14th October 2009, 11:00 PM   #6
Floyd
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Join Date: Sep 2006
Posts: 459
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Hi Unregistered.
Yes you are right. I think even my old Garmin 12 (from circa 1997) used doppler for speed read out,but did not store speed info. All its future speed measurements were dS/dT and hence reliant on positional date . (Including trak logs)

There` a number of ways you can see this to be case but main evidence is from Garmin`s accuracy data .Even on older units accuracy claimed for speed read out (on unit) was way better than that claimed for position. (and constant) If speed was dependant on position its accuracy would not be constant and at best could only match positional accuracy. (ie bigger distances would give more accurate speed figures; which they dont.) (Its an old argument and has been aired on here a few times)

Vbox have been building a speed measurement unit for use in F1 (and others) for years. One model totally relies on doppler from GPS time signals.(Particular unit gives no popsitional data though)

Its only been a matter of time for GPS builders to start recording the doppler speed data. (One chap at Garmin told me units could not operate without knowing speed before positional data was calculated ???)(ie its the first thing unit does???!!)

PS
Just ordered Genie/Aquapak/card
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