Wrong total distance for activities longer than 167.76 km [Bug 10]

[gps_techie]

Some observations on 167.77km bug in eTrex SE (FW 4.20)

First, impact of 167.77km limit to various display measures. When TRIP ODOMETER reaches and caps at 167.77km, then:

• MOVING TIME stops increasing, while STOPPED TIME continues to increase (regardless of actual device movement). MOVING TIME increases only when distance increments.

• MOVING AVG stops changing at 167.77km (because both distance and MOVING TIME do not change).

• OVERALL AVG continues to decrease (because distance is fixed and total time := MOVING TIME + STOPPED TIME increases).

• ETA is partly wrong because it is calculated as actual distance to destination (accurate) divided by MOVING AVG (inaccurate).

Various measures become distorted with distance limit bug (although one can interpret them as still being "half-true").

Second, when activity with 167.77km bug is saved and TRIP ODOMETER is reset to 0 without turning eTrex SE off, TRIP ODOMETER of second activity starts with 0 and does not increase beyond 0. I.e., once 167.77km bug is reached, all new activity logs are distorted (TRIP ODOMETER, MOVING TIME, etc.). Turning device off helps to reset distance accumulation.
This points to some memory variable overflow and not just individual distance statistics overflow.

I haven't heard any news on FW development.

[Przekątny]

• ETA is partly wrong because it is calculated as actual distance to destination (accurate) divided by MOVING AVG (inaccurate).

The error "167.77 km" has no effect on the ETA, the ETA has nothing to do with the activity registration.

[gps_techie]

• ETA is partly wrong because it is calculated as actual distance to destination (accurate) divided by MOVING AVG (inaccurate).

The error "167.77 km" has no effect on the ETA, the ETA has nothing to do with the activity registration.

I noticed strong effect and I experienced it first hand on eTrex SE. Calculation result looked exactly like "actual distance to destination"/MOVING AVG. If first 167.77km were traveled at slow pace, ETA would be hopelessly pessimistic all the way to the destination.

[Przekątny]

We have two types of ETA with different mechanisms of operation, ETA for route, you didn't write about that one.

The second mechanism of determining ETA (without routibg) does not take into account
the distance we actually have to cover, it is determined based on the instantaneous
speed of approaching the destination, not on the basis of walking pace.

[gps_techie]

I used eTrex SE feature GO TO and selected distant waypoint. eTrex SE plots straight line from current location to waypoint, shows distance/direction/speed/ETA on separate navigation screen. Based on these values ETA is calculated as [actual distance to waypoint] / [MOVING AVG].

For example, say you traveled 480km in 6h, but first 170km took 4h. Now set eTrex SE to waypoint 200km from your location. Then ETA will be
[200km] / [MOVING AVG] = [200km] / [170km/4h] = [200km] / [42.5km/h] = 4h42min (incorrect) or
[200km] / [MOVING AVG] = [200km] / [480km/6h] = [200km] / [80km/h] = 2h30min (correct).

To be clear, main issue is trip odometer 167.77km bug. Incorrect ETA is a secondary effect of this bug.

[Przekątny]

For example, say you traveled 480km in 6h, but first 170km took 4h. Now set eTrex SE to waypoint 200km from your location. Then ETA will be
[200km] / [MOVING AVG] = [200km] / [170km/4h] = [200km] / [42.5km/h] = 4h42min (incorrect) or
[200km] / [MOVING AVG] = [200km] / [480km/6h] = [200km] / [80km/h] = 2h30min (correct).

ETA is a determination of the time of arrival at the destination in the future, not after the fact.

But OK.

ETA for the route takes into account the actual distance to the destination, ETA is determined depending on the means of transport (type of activity), e.g. for a pedestrian the assumed speed is about 4.7 km/h, for motor vehicles to determine ETA speed restrictions are taken into account (not necessarily according to road signs) but assigned to individual road sections when creating the map.

[javawa]

Of course there is no ETA after the fact (you know exactly when you arrived, so the "E" is not relevant anymore), but you are missing the fact that the ETA is constantly recalculated during the activity. The current (average) speed will be taken in account for that.

for motor vehicles to determine ETA speed restrictions are taken into account (not necessarily according to road signs) but assigned to individual road sections when creating the map.

That will never happen on the eTrex SE, so that is not relevant in this case.

[Przekątny]

That's right, in Etrex Se there is no possibility of determining a route with a routing, so let's go back to my previous post ETA determined for a route without routing.

For a route without routing, the time of arrival at the destination is determined, it does not take into account the actual distance that we have to cover.

@ gps_techie

The time of arrival at the destination is determined on an ongoing basis, you cannot refer to a previously established ETA, you are at a specific point on the route, such is the specific time of arrival at the destination that you see on the screen.

The ETA is determined only for the section that remains to the destination,
it does not take into account the distance or time or speed for the section that has already been covered.

[gps_techie]

Not sure where assumption to treat ETA as fixed value comes from. Of course it is changing with time, as ETA is momentary measure (estimate of arrival time based on current distance to destination and current MOVING AVG). Distance lowers with time, MOVING AVG changes (hopefully) and in the very end of travel ETA converges to current time - the less distance, the less error.

Problem arises when due to 167.77km bug MOVING AVG becomes fixed. So instead of ETA sequence with values
[200km]/[80km/h], [120km]/[92km/h], [100km]/[95km/h], [40km]/[98km/h], [10km]/[99km/h], ...
you get incorrect sequence with wrong denominator
[200km]/[45km/h], [120km]/[45km/h], [100km]/[45km/h], [40km]/[45km/h], [10km]/[45km/h], ...
as MOVING AVG is no longer updating. Try this with eTrex SE in GO TO navigation mode.

[Przekątny]

I assume that you have the activity recording enabled after starting the device - disable it and check what happens with the average speed of movement after exceeding 167.76 km.

Does exceeding 167.76 km affect the current speed and distance to the destination?

When hiking or driving on a road route, distance and a constant, instantaneous speed (not average speed) are used to determine the current ETA.
Similarly, when hiking according to the route on off-roads, the constant, instantaneous pace of the march is taken into account.

Constant, instantaneous pace - speed with a small increase or decrease maintained for several dozen meters (at this moment I cannot be more precise).