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Is Trip Odometer accurate???


res2100
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I have a Sportrak Pro and am wondering if the Trip Odometer is accurate? Here is what we were doing:

 

Walking through the forest on winding trails going up and down hills, etc. Most of it being tree covered. We walked around the park on these paths and it measured about 2.8 km that we walked. However, when we drove on the road a "straight distance" to the further points north and south of where we walked it was 1.2 km (x2 = 2.4 km). certainly with all the winding trails and inclines and declines would be more than a mere .4 km? Based on this we had exepected the GPS trip odometer to show about 4.5 km and not just 2.8km. Does it lose some of it's signal in the woods and therefore not keep track of the distance travelled? Or is the 2.8km that it said we walked truely accurate.

Also, does it take into account going up and down hills?

 

http://ca.geocities.com/rsab2100/pond.html

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Several months ago, a fellow cacher told me that on hikes along the Appalachian Trail the odometer on his gps recorded distances pretty consistently at 20% less than the distances listed in the official trail guides.

 

I haven't checked my Vista against any trail guides, but the odometer on my Vista does record less than the two pedometers (one mechanical and one digital) I sometimes carry ... but then again, climbing up steep hillsides would shorten the stride and affect the pedometers' accuracy.

 

In tests in the car, I have noticed that on a routine commute my cars have always consistently indicated at 48 miles indicates 3 or 4 miles less on the Vista.

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Would the refresh rate have something to do with it also? I have my GPSr set on battery save mode, which means (I think) it only updates every 1 second or so. On a curvy track, this would mean lots of tiny straight line short cuts.

 

During bad signal, the reported position can jump around by a bit, even while standing still. Once it was 50 m. Would this be counted as having walked 50 m?

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I have noticed that the faster you go, i.e., in a

car my GPSr trip computer is more accurate, as long as I have a good fix, I've reset my odometer

on my car and gps, and drove, there was mabe a 1/2

of a 1/10 mile difference. good enough for me. As far as track goes, the vista has time and distance

record modes, when I hike, I set it to record every 15 seconds, when driving I set it to distance, every 1/4 mile. It works great for me. icon_cool.gif

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We've got a Garmin Emap we use for geocaching as well as recording trail miles for horseback riding. We've found that when we ride in the open, the odometer's fairly accurate. When we're under the cover of trees it seems that the odometer on the GPS shows low mileage. But what is interesting is that if I save the track of our trip, it indicates a higher mileage. I assume that the odometer just drops the distance when satellites are shadowed, but the track length reflects the distance between good fixes. Anyone else notice similar stuff?

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Doug M M P,

Have you updated your eMap to a recent firmware release (2.74 or higher)? The older firmware would just drop mileage cumulated during signal loss but now it adds in the straight-line approximation for those periods. I no longer see significant discrepancies between the trip odometer and the Saved Track distances on bike rides and hikes. The distances also match well with those from properly-calibrated cyclometers and wheel-measured trail lengths.

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Doug M M P,

Using battery-saver mode will make the unit more susceptible to signal loss, but I'm still puzzled as to why your unit is recording substantially less mileage on the odometer relative to the Saved Track. I've watched the odometer on mine during periods of signal loss and seen that it stops cumulating but then jumps up to a higher value when the signal is regained. So it is adding in the straight-line distance travelled during the time that the signal was lost. The Saved Track length also includes a straight-line segment for those times and should show about the same length; and that's what I've been seeing. The distances may vary by a few hundredths of a mile, but no significant differences the way there were with earlier firmware when the odometer totally ignored distance travelled during signal loss.

I'll have to try it in Battery Saver mode and see if that also affects the odometer algorithm.

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