Re: Odometer vs Track Log ???

In message <memo.20070821220907.5272B@xxxxxxxxxxxxxx>
mick@xxxxxxxxx (Mick) wrote:

"Jon O'Brien" <Jon@xxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Does the track log take altitude into account and could going up and
down
hills account for the difference?

That thought just entered my head also..


No unless you are doing a lot of vertical ascents and descents you won't
add much to distance horizontally. Remember even a continuous 30 degree
slope is only going to add the ratio of 2 to the square route of 3 i.e
approximately 2/1.7 How often do you encounter long sections of 30
degree slopes on your walks?

The error is I suspect in the different algorithms used to estimate the
distance. The track log distance is essentially the sum of all the
individual tracks between each individual point (this can of course also
include spurious points where the GPS was unsure of your location). If
you load the track log into an editor such as GPS Utility you can look
down the list of points and frequently see ones that look odd, e.g. they
report a speed and distance that you couldn't possibly have achieved at
that point in time. These will tend to over estimate the real distance.

The trip odometer tends to try and smooth these irregularities out I
think. Also if you switch the GPS off and move to a new location and
switch it on again, the trip log tends to ignore that section, but the
distance on the tracklog assumes a straight line of travel between the
two points.

In other words both methods of estimating your distance travelled have
different possible sources of error and thus are unlikely to be in exact
agreement.

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

Relevant Pages

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