GPSrChive Discussion Forum

I use two Garmins: an eTrex 10 and a GPSMAP64. Yesterday, I got a reading from the eTrex of 15km for a bushwalk. The MAP64 returned 16.2 km for the same hike. The walk was mostly undulating through light – medium density forest.

Having had the two units for several years, this discrepancy was not unexpected. The MAP64 regularly shows a greater distance for walks in forested and/or hilly country. However, on a flat beach and walking more or less a straight line, the eTrex and the MAP64 almost always agree. On the rare occasions when there is a discrepancy, it's only .1 or .2 km.

Am I correct to assume that the MAP64's capacity to acquire satellites when walking in cover and/or hilly country exceeds the capability of the eTrex 10, or am I missing something?

If you can share the tracklog from each device I can show you why the discrepancy exists.

TY! Logs are here: https://drive.google.com/drive/folders/ ... sp=sharing

Just tried Create Garmin Adventure in Base Camp. The distances shown are 15.0 (that was what the etrex 10 recorded) and 15.3. The GPSMAP 64 reading on the screen at the end of the walk was actually 16.2. I don't know why.

I have examined the tracklogs from each device.

The eTrex 10 tracklog is 836 track points long with a total point to point distance of 14.97 km.
The GPSMAP 64 tracklog is 942 track points long with a total point to point distance of 15.27 km.

As the GPSMAP 64 tracklog is more than 100 points longer than the eTrex 10 tracklog, it makes perfect sense it is showing more distance.

While I do not know what recording interval you have selected on each device for tracklog recording, it appears they are very similar. What do you have configured for each device?

There are multiple possibilities to explain why the GPSMAP 64 indicated a total distance of 16.2 km on the screen at the end of your 15.3 km walk, the most likely being that the Trip Computer and Track Log recording intervals were not identical, or that the Trip Computer and Track Log recordings were not reset simultaneously, or some combination of each.

Please see GPSrChive > How To... > Tracks > Track vs. Trip Computer for a detailed explanation.

Thanks for checking. The different number of points sampled explains the discrepancy. The track settings on both devices are Auto, Normal.

On the MAP64, Clear Track and Trip Data = Reset Both. There is no comparable setting on the etrex10.

What I think you're suggesting is that selecting Track Manager => Current Track => Clear Current Track doesn't reset the trip data. If so, to fix the problem I need to use Setup => Reset => Reset Both at the start of each walk. Would you agree?

Yes, try that, and also try setting both devices to record based on time, and use the exact same interval for each, so that the tracks will each record at the same rate regardless.

The Trip Computer records at 1 point per second, but this can create a very large track file pretty quick. You may have to experiment to find the settings that are the perfect compromise for you, with just enough detail but not too many track points.

Both units now set to record based on time, with a 30 second interval. Let's find out.

Again, many thanks.

Please understand that this means the Trip Computer will log 30 data points for each single data point saved in the Track Log recording, which will result in the Trip Computer reporting a greater distance traveled. The longer the recording, the greater the discrepancy.