Re: Calibarating my computer.

In message <g8kgit$8rc$03$2@xxxxxxxxxxxxxxxxx>
Tosspot <Frank.Leake@xxxxxxx> wrote:

Mike Clark wrote:
In message <b8noa4pab6c06v2p6e7ts1nt72gbqqkrfi@xxxxxxx>
Ace <b.rogers@xxxxxxxxxxx> wrote:

On Wed, 20 Aug 2008 18:24:14 +0200, Tosspot <Frank.Leake@xxxxxxx>
wrote:

Ace wrote:
Others have said it, but I'm not sure you've got the message so it
bears repeating/rephrasing: the GPS calculates speed and distance on
an interval basis, so it looks at your position and compares it with
that of 1/4 of a second ago[1].
'S funny, I thought it was by doppler measurement.
Not sure how that'd work; for speed, maybe, but not for distance.

I realise I did say speed in the previous post, but I was really only
thinking about distance, honest!


A GPS carries out a position velocity and time (PVT) calculation on the
available satellite signals. Thus the velocity measurement is part of
the calculated solution for the current calculated position. To get
distance, as others have said, the device carries out a secondary
calculation of the distances between the recorded track points. However
there is often a difference between the odometer read out on the GPS
compared to the distance summed over all track points if you save the
active track log to a suitable computer program. I assume that the
manufacturers have included some kind of smoothing algorithm in the
calculation (this is certainly true of the three different Garmin models
that I have used).

That sounds like chapter and verse to me, you got a definitive URL to
stop us having this discussion again?

There are some good links from Alan Murphy's GPS Utility website (this
incidentally is a useful piece of software that I use for analysing,
manipulating, and archiving my GPS track logs)

see http://www.gpsu.co.uk/

For an explanation of the PVT calculation I'd recommend Dale DePriest's
website.

see http://www.gpsinformation.org/dale/theory.htm


Mike
--
o/ \\ // |\ ,_ o Mike Clark
<\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
"> || _`\<,_ |__\ \> | reader in immunology, antibody engineer and
` || (_)/ (_) | \corn computer user"
.

Relevant Pages

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  • Re: Calibarating my computer.
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