Arc mini not a solution to the missing data problem

I’ve had problems on the past apparently related to IOS closing Arc, leading to periods of missing data. It was also combined with spurious location data around a “home” location (up to a kilometer away, usually in one or two favoured directions (so the bogus points would often be in a line), which may or may not be related.
I found that one or two resets of my iPhone 11 seemed to solve the problem, so I now reset whenever I see the problem.
I’ve installed Arc Mini as a solution to the data gaps, but it seems that is not working. I had two gaps today, one of 20 min, one of 55 min. I had no messages about the either app being killed. Multiple resets have not fixed the random location data either. I’m attaching a couple of screen shots to illustrate. The first one shows spurious movement when I was at the upper location all morning. The second shows missing location data on a short loop in the car.

I’d be interested to know if you have any ideas, or comments on whether Arc Mini is helping

For this, the first steps are to make sure your phone has the tools it needs for achieving reliable location data accuracy. Make sure wifi is on (it doesn’t have to be connected), the phone isn’t in Airplane Mode, and Arc and Arc Mini have “Precise Location” permission in the phone’s Settings → Privacy → Location Services → Arc / Arc Mini.

Beyond that, if your phone is still producing location data that drifts over hundreds of kilometres, that means the phone simply isn’t capable of maintaining reliable location data at that location. At that point, the next steps are to teach Arc to recognise when the phone has lost its grip on reality, and to deal with it automatically.

To do this, go into the Individual Segments view of the visits with bad location data. Then identify the segments that are more than about 100 metres from the real location, and mark them as “bogus”. For segments that are within about 100 metres of the real location, and you were stationary at the time, instead mark them as “stationary”.

These two actions will train two different systems: 1) The bogus classification will allow Arc to detect extreme drifts in location data at certain locations, and automatically mark it as bogus in future. 2) The smaller drifts that you marked as stationary allow Arc to determine a “Trust Factor” for location data around that place, learning to what degree the data tends to drift. The more drift that happens at that location, the less the recording engine will trust what the phone says, and will filter it more aggressively.

Make sure you’ve added the Current Item home view widget to one of your home views, so that you can see the little green/red dots, to catch cases where iOS has killed off both/all apps. Having both apps alive gives you double protection, but iOS will still periodically kill off both apps, as the mood takes it.


Thanks for the quick reply.

Previously Arc had recorded location accurately at this location. Wifi is on, and both Arc and Arc Muni have precise location enabled.

I have been marking the random locations as bogus. I had not appreciated the recommendation to use “stationary” for points within 100m - I have been marking all as bogus.

I’ve enabled the widget. And I’ve reset the phone several times. It seems to be working ok today. All these errors have occurred after relocating from France (some 700 miles away) after a couple of months at a single location. I had similar issues on first arriving in France, so I suspect these big moves may be upsetting the learning engine for a while. Is that possible?



Yeah it’s not messaged in the app anywhere. I’ve actually built a mini tutorials view into the app, for mini articles on things like this, to help get the best out of the data and recording. But it’s been stalled on having time to write the articles. Ironically, I instead end up spending more time explaining the same things repeatedly on the forum instead :joy: I really should finish up the tutorials/mini articles stuff.

There’s a couple of things going on with very long visits (eg lockdowns or movement restrictions that lead us to end up staying at home for multiple days). The first is within Arc, and the second is within iOS itself.

Within Arc, there’s a system of predicting the probability of you leaving the current place, based on time of day, duration of visit, and some other factors. Longer visits make those predictions less reliable and less useful. The result of that is that Arc becomes less accurate at quickly restarting recording when you do leave the house.

Though that inaccuracy should typically be less than 2 minutes, although it can be worse if Arc goes into “deep sleep”, where it effectively turns off completely, based on the prediction that you’re definitely not going to leave the house for 6+ hours. (During deep sleep state, Arc has several wakeup call systems, to get it restarted before your predicted leaving time. But it’s a gamble, because you could leave before the predicted time, and Arc will then miss maybe 5+ minutes of recording, until less accurate wakeup systems kick in).

But that doesn’t explain the weird, excessive location data drift during these long stays at home. That’s a quirk of iOS itself. I haven’t done extensive testing on it in a while, but the effect is that for some reason iOS / the phone’s location data sometimes gets significantly worse during long stays. I can’t guess what underlying system is causing that - it doesn’t seem a reasonable energy use optimisation - but enough people have seen it that it’s a definite pattern :man_shrugging:t2:

Aside: iOS also has an underlying location accuracy improvement system, based on wifi hotspot triangulation, that improves the accuracy of location data at new places over the first few days. But that shows itself as typically low quality location data in the first 1-2 days at a new place, which then becomes increasingly accurate and refined after that. So that system doesn’t appear to be related to this problem, as what we’ve seen during lockdowns is effectively the opposite: the location data gets worse over time, rather than improving over time.

@matt @Nigelb

I’ve having the spurious location data around a “home” location recently too.
I’ve moved to a rent place, and after I wake up there will be some Airplane, car, etc bogus data during I was slepping. WIFI+CELLUAR+PLUGIN of my phone.
Not for every place but I’ve found out it seems to be unstable after iOS 15. Can you may be dig a little to see if there is any change on ios 15 side or bug?

When you do a major version iOS upgrade, often your wifi hotspot triangulation database is wiped and started fresh. This is especially common if you were also using the iOS betas, because during the betas they might’ve been making a bunch of changes to the data and databases, so when you install the final release version of iOS 15, it will wipe out those databases to make sure they start fresh, with no bad data from the beta period.

It’s easy to tell if that’s happened, because you’ll see location data get really messy in places where it was previously very stable. Then after a couple of days it’ll settle down, and start looking sensible again (ie after the phone has filled out its wifi hotspot triangulation database again for those places).

The nasty situations are the ones where the phone never gets to a good level of location data quality/accuracy at certain places, even after it’s fleshed out its wifi hotspot triangulation. That’s especially common in high-rise buildings, where you’ll only have line of sight out one side of the building, and also potentially lots of GPS reflection/distortion from surrounding buildings.

Though that’s again unrelated to the problem of location data getting mysteriously periodically worse at places where it was previously stable, especially during long visits (eg during lockdowns). The exact causes of that one are still a mystery.