Etrex 30 vs Etrex 10 Odometer discrepancy

[+PhantomODOpera]

I have an etrex 30 (v2.8) and my hiking partner has an etrex 10(are there updates available for this?). At the beginning of each hike we both reset our etrex Odometers and off we go. At the end of the hikes our Odometers differ greatly. I can understand small differences, but they differ what I consider a lot. For example today my etrex 30 showed 8.53 miles and hers showed 5.61 miles. We were together the whole time. another example, last weekend my etrex 30 showed 6.3 miles and hers showed 4.8

Any idea why such a large discrepancy?

Which one should we believe?

[tr_s]

The new eTrex firmwares (20/30) is what I consider a "hasty throw-toghether" from what I've seen - so not surprised that yours are differing greatly. It's a shame, but it seems to be Garmin's new paradigm of software and the basic features are not very consistent from my experience. They got many of the advanced features - map drawing and so forth - basic things like distance calculation and route following do not work as expected.

 

I do suspect the main problem lies with what distance deltas are used for calculation. Think about it: Does a severe drunk or an athlete runner make the same distance on a street, counting every step? No they don't - the drunk can easily make twice as much of a distance as (s)he wiggles back and forth on the street.

[seldom_sn]

Try comparing the tracklogs in BaseCamp. Tracklogs are generally more reliable than trip odometers.

[+user13371]

Some questions and thoughts:

 

1) Compare track settings on both models - are they the same? See page 7 of the eTrex 10 manual. Maybe the options of Auto, Distance, or Time might affect the accuracy of the recorded track and feed that back into the odometer reading.

 

2) To expand on something seldom_sn mentioned, Basecamp (or Google Earth) can give a more accurate idea of track length than the odometer does. That can tell you which one to believe (as can local knowledge). By your own after-action analysis, which device had a more accurate odometer?

 

3) Are both devices running the most current firmware?

 

4) Be careful whose advice you take. Would you trust someone who has posted an order of magnitude more messages complaining about his GPS than he has found geocaches? 'Tis a poor craftsman who blames his tools.

 

Edited July 1, 2012 by user13371

[+Atlas Cached]

I have an etrex 30 (v2.8) and my hiking partner has an etrex 10(are there updates available for this?). At the beginning of each hike we both reset our etrex Odometers and off we go. At the end of the hikes our Odometers differ greatly. I can understand small differences, but they differ what I consider a lot. For example today my etrex 30 showed 8.53 miles and hers showed 5.61 miles. We were together the whole time. another example, last weekend my etrex 30 showed 6.3 miles and hers showed 4.8

Any idea why such a large discrepancy?

Which one should we believe?

 

Compare settings on each device in [setup | Tracks | Record Method] and [setup | Tracks | Record Interval].

 

Are they identical?

[tr_s]

posted an order of magnitude more messages complaining about his GPS than he has found geocaches? 'Tis a poor craftsman who blames his tools.

 

Geocaching is not a general hobby of mine. I just happened to place the #2 geocache in europe and have since retained my credentials here. Since this is one of the top GPS technology forums as seen from google it seemed fitting to join in. Never had the need to join into a forum to bash my prior three Garmin receivers as they have shown a pretty much flawless performance - my 1999 eTrex still does!

 

Anyway, I don't think the track log interval setting feeds back to the trip/odometer in any way... Just seems weird that it would do so. How the tripmeter calculates distance is probably hardcoded in the unit's software. It would be strange if Garmin actually uses different code snippets for this in the 10 vs. 20/30, but what do I know.

 

If the fault doesn't lie with the GPS maybe Phantomodopera's hiking partner has less of an inclination to "fidget around" when hiking? Interesting test: Put both GPSes in the same jacket pocket, reset the tripmeters at the start of the trail and see if they still differ notably at the end. A few percent would be normal due to noise and whatever, not 30% like you seem to report...

Edited July 1, 2012 by tr_s

[+user13371]

Interesting test: Put both GPSes in the same jacket pocket, reset the tripmeters at the start of the trail and see if they still differ notably at the end. A few percent would be normal due to noise and whatever

That's interesting for a different reason than comparing walking styles. Rather than "a few percent" difference, jamming to GPSRs into one pocket might render one or both of them wildly inaccurate. Depends on how good or bad noise rejection is - but in the past I've seen some that would bug out only when only a foot away from another unit.

 

I don't think the track log interval setting feeds back to the trip odometer in any way

I don't know if it does either; it's just something to test. More I think about it, I'm leaning more towards firmware differences. That whole "improvements at low speeds" deal they've incrementally been working on. I'm expecting the unit with the under-reporting odometer has older firmware.

Edited July 1, 2012 by user13371

[tr_s]

You're right - it's not a very good idea to jam them so close to each other - maybe side pockets on opposing sides of the same backpack would be ideal! From my limited experience however, it was never a GPS that threw off another, intended transmitter equipment such as as a laptop or notebook with 3G/Wifi seemed to be much worse... putting a high sensitivity GPS on top of a Wifi enabled laptop seems to make the signal bars fade to a fourth or die out altogether.

 

Very case specific of course how it will play out - types of receivers, system frequencies, rf isolation, phase of moon, etc.

Edited July 1, 2012 by tr_s

[Suscrofa]

Some questions and thoughts:

 

...

 

4) Be careful whose advice you take. Would you trust someone who has posted an order of magnitude more messages complaining about his GPS than he has found geocaches? 'Tis a poor craftsman who blames his tools.

 

 

He gave a valid explanation showing an understanding of the issue !

 

Having a lot of "found" doesn't make a GPS expert but being an engineer is a good way to start !

Edited July 1, 2012 by Suscrofa

[+user13371]

Wait, Suscrofa, you mean you're not going to blame the odometer problem on imperial/English measure rather than more sensible metric units?

 

[39_Steps]

I recently started riding a bicycle again, for the first time in 15 years or so of intermittent consumer gps use. In reviewing my bike track logs over known road vector distances on city streets in my computer mapping app, I found that the gps track log distances compared quite well with calculated (route) distances at bicycling speeds, unless I walked into the back of a store to get a donut along the way and degraded the gps signal with the gps secured in a pocket.

 

In short, a gps mounted on a bike that is ridden on streets without too many trees or urban canyons can be about as useful a method for checking accuracy of odometer distances or other derived info fields as I have found. My bike tracks tend to not meander as much as my hiking tracks, even when walking the bike. GPS odometer info vs. Automobile odometer info at higher speeds could be useful as well, but I am usually too busy driving to notice.

 

[Delome PN-60 at default one (1) second track point intervals, as viewed in Delorme Topo9 North America Profile View]

[+user13371]

39Steps, your experience matches mine. Though not to the degree some have noted -- the slower I'm moving, the less accurate the odometer distance is, and always underreported. This has been true to some degree of every GPS I've ever owned, several different models and brands, and I take it for granted.

 

I've always just assumed the odometer is "rouding down" the distance between each sample at 1 second intervals. At slower speeds (shorter distance between samples) it's more noticeable.

 

As I said, I take SOME under-rpoerting at low speeds for granted. It's jmore interesting to me that the OP has two similar models from Garmin that show such a striking difference along the same track.

 

I'd put money on that being a firmware issue - one being more up-to-date than the other.

Edited July 1, 2012 by user13371