InReach Explorer Plus - High Tracking Mileage Readings

Hello fellow outdoors people,

I've been using my InReach Explorer + for a while on backpacking trips and have found a bizarre behavior. Sometimes, the daily total mileage hiked while tracking is on all day (10 min send, 1 min log) is higher than expected. For example I did a section of the Ouachita Trail that was expectedly about 12.1 total miles according to the guide map on Guthook, and my iPhone 12 kept up with that mileage, but at the end of the day the Garmin showed 16 miles travelled. I'm aware of how mileage can be less if traveling faster (on a bike, etc) along switchbacks, but don't see how it could be more and by 4 miles. I've also noticed that without fail, when tracking is on and I view trip info on the handheld device, the Speed Max and Moving Average is always identical. In the example above, the speed max was 4.4 mph for the full 10 hour hiking day, and the Moving Average matched that all day long (or for as long as that was the max...when the Speed max was lower then the average of course would match that same lower number).

Thanks in advance, I appreciate it.

0 twolpert over 3 years ago

Your results will be closer to reality if you log at shorter intervals. But this does eat battery.

Particularly if the maximum speed is higher than is reasonable, you are probably seeing the result of high-speed "excursions" off the the path you actually travelled. These occur in challenging conditions (where multipath reception is likely). The unit does its best to guess at which of several readings from the same satellite is the "real" one. Sometimes, it changes its mind as conditions change. This results in a relatively large shift in calculated position virtually instantly. When this shift is recorded, it will probably add a few hundred feet to the recorded distance, and will be at a relatively high speed, which affects maximum speed as well as moving average.

Personally, I ignore moving average - especially at long logging intervals. This is not computed the way we all think it is. In particular, total distance traveled divided by time moving (assuming the unit got THAT right) is not equal to moving average speed. All GPS units compute this by averaging the speeds on individual segments (between points).

0 Unstoppable over 3 years ago in reply to twolpert

Thank you for the reply! Makes sense on how the unit calculates moving averages, and multipath reception also makes sense.

Regarding the shorter log intervals, are you referring to shorter than 1 minute? I would think that when hiking, 1 minute is sufficient to maintain within a very small degree of variance (where as biking/moving faster it may not be), but I'm also nowhere near as knowledgeable on the GPS system than you and others here.

I think in my case there may be another influence, here's a scenario. There was a particularly slow moving average section of about 5 miles switchbacking on relatively flat ground through mud, 8-9 water crossings, lots of rock gardens, etc. Because of the terrain it made for what turned out to be 1.2 to 2 mph. At the beginning, my moving average showed 4.4 mph (which was easily achieved, and was real, going down part of the mountain earlier in the morning). At the end of those 5 miles, moving average still showed 4.4 mph. Then we had a 2.7 mile climb up the next part of the mountain, roughly 1,200 feet elevation gain, so it was steep at times. We did that in in about 2.5 hours. At the end, moving average still showed 4.4 mph. That 7.7 miles was just a bit over half of the day's mileage hiked, so I would have expected the moving average to lower after averaging all of the tracking segments.

I just now checked the data sent to MapShare, and oddly enough, it looks more accurate there. Though it has much higher max speeds per day tracked (8mph, so probably the off path excursion you mentioned earlier since there's no way we could have walked 8mph), the average is within reason. One day is very low but it also shows the time tracked as a full day rather than the 10 hours we went, so I probably forgot to turn tracking off, though the next morning I was able to start tracking like usual without having to turn the prior day off first. But for that long day, it showed the mileage as 14 miles instead of what the device showed day-of as 16 miles.

I wonder if a factory reset would help. What do you think?

0 Unstoppable over 3 years ago in reply to Unstoppable

Figured out the distance travelled, and probably the max speed as well (but not the average as shown day-of on the device). With another set of replies that you provided to a Mini owner, and a subsequent reply by a Garmin employee on improving tracking stats, my results are explained by GPS drift while taking breaks (compounded by moderately full tree canopy at times and grey skies). Makes total sense. For anybody else reading this, check out the article here and Twolpert’s awesome replies on the forum in general (his reply here is very good as well).

Now just need to find out why moving average stays “stuck” as the max moving speed for the track session, only on the device. MapShare corrects it.

support.garmin.com/.../

0 Unstoppable over 3 years ago

For anybody else reading this, I contacted Garmin support for the average moving speed part. Makes total sense now, here's the chat transcript that Micah said I could add here:

[10:10:42 AM] Micah So I think what's happening is when moving 1.5-2 mph or less the explorer thinks that you're stopped, so it doesn't add that section into the average moving time. but the explore site is designed to "Clean Up" tracks once they're uploaded to give you a more accurate recording which is why you're seeing different values between there and the device
[10:13:35 AM] Me That would make a lot of sense, since I only really started using the Garmin on this specific trail, which has a ton of rock gardens, elevation changes, water crossings at times, etc. Moving 2mph or slower is common, and probably at least half the day due to that. So, you're saying that even if auto-track is turned off and I haven't paused tracking, which essentially tells the device "keep tracking me", it still thinks on its own and ignores slower moving speeds?
[10:14:58 AM] Micah That's correct, it'll keep placing the track points, but it doesn't adjust the moving speed, because it thinks that those slow speeds are just GPS drift
[10:18:32 AM] Me Ok, so it's a built in mechanism to minimize GPS drift effects that unfortunately also affects this particular situation. Are there any good workarounds you can suggest, other than manually calculating an average moving speed? The metric is helpful for when figuring out, along the hiking day, how much further is realistic to move to make it to a suitable camp before sundown. I use another app that has all of the reported campsites along the trail, so we figure out our daily destination as we move.
[10:19:50 AM] Me Manual calculation is fine, just requires keeping mental note or writing down mileage and current time at various points throughout the day. It would be so much nicer to just see it on the screen, hah.
[10:20:42 AM] Micah Unfortunately, there isn't a workaround for that device, the only solution is that the explore website will try to correct those miscalculations, but on the device side there aren't any settings that can be changed to stop that from happening.
[10:25:00 AM] Me Ok, thanks. If a feature request can be made to help that metric be more accurate at those slower speeds, I'd like to make that feature request, but I do understand the reasoning behind why it doesn't and that it may be a challenging algorithm to introduce. Potentially adding a setting for Trip Type that one can set before tracking, such as "Biking", "Backpacking", "Running", "Boating", etc, would help introduce a new metric of expected speeds and distances that the algorithm can then use when compensating for GPS drift. Compensate for for faster moving activities, less for slower, and then for any drifts that are longer distance than realistic for that activity, ignore it (such as, if when backpacking a device all of a sudden moves 300 feet in a few seconds, ignore it). Can that feature request be made?
[10:26:00 AM] Me That was meant to write, "Compensate more for faster moving activities, less for slower"
[10:27:32 AM] Micah I can make a request for that feature, just a moment while I pull that up.