Garmin GPS - Why would track distance be different from odometer distance?

Author

Why would track distance be different from odometer distance?

Xxxxx

2006-12-23, 10:33 pm

I go for daily walks/runs, usually 6 to 10 miles. I have a pedometer that
appears to be well calibrated to my average stride, and its distance is
usually within 1% of the actual distance I walk.

Yesterday, I decided to try out my new 76CSx, thinking its odometer would be
more accurate than my pedometer. I was disappointed to see that it said I'd
walked only 4.8 miles, when I had actually walked 6.2.

Today, I tried again. But, this time I turned tracking on, so I could see
where it was going wrong. Today, I walked 7 miles, but the 76's odometer
said I'd gone only 5.7. Also, although I walked for over 2 hours, the 76's
"moving" time said I'd been moving for only 1h40m. (My pedometer logged 127
minutes of aerobic walking, agreeing with my watch.)

I loaded the track into MapSource and discovered that it agreed exactly with
my pedometer!

The 76 was in my back pocket, antenna up.

Is it likely that the difference was due to occasional loss of satellite
reception as I walked? Since the track goes from point to point, it
wouldn't lose any distance, although some track points would be further
apart than expected.

If it's losing reception as I walk... this is not great news, since there
are no canyons or tall buildings where I walk. I hope I don't have to start
wearing a tinfoil hat to use as an external antenna.

--
Nada y nadie

peter

2006-12-23, 10:33 pm

Xxxxx wrote:
> I loaded the track into MapSource and discovered that it agreed exactly with
> my pedometer!
>
> The 76 was in my back pocket, antenna up.
>
> Is it likely that the difference was due to occasional loss of satellite
> reception as I walked?

You should be able to see if the recorded track in MapSource is
continuous or broken into pieces with gaps where reception was lost.
If you only have one continuous Active Log then loss of reception isn't
the problem.

I still use my old (7 years) eMap and rarely see more than a 1 - 2%
difference between the odometer and the tracklog on either hikes or
bike rides (and both are generally in very good agreement with trail
guides and road surveys). But back when it was new there were
frequently much larger discrepancies. Subsequent firmware releases
fixed the problem.

> If it's losing reception as I walk... this is not great news, since there
> are no canyons or tall buildings where I walk. I hope I don't have to start
> wearing a tinfoil hat to use as an external antenna.

No tinfoil in my hiking cap, but I did sew a little pocket inside the
top of it for my external antenna for use in areas with lots of foliage
cover. It's also nice to be able to put the eMap in any convenient
pocket without worrying about the antenna orientation.

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