The basic rule of thumb I use is: If it’s less than about 100 metres from the real location, mark it stationary; If it’s more than about 100 metres away, mark it bogus.
Yep, exactly. So if the drifting data was too far away, and you mark it as stationary, it’s going to firstly expand that Visit’s radius out to possibly an absurd size, then incorrectly consuming some trip details on either side. And secondly it will end up expanding the Place’s orange radius out, which will potentially mess up auto place assignments on subsequent visits.
Hence my vague 100 metres rule. (That I tend to break sometimes when the mood takes me. If I feel like a specific Visit’s radius could be / should be cleaner and smaller, I’ll edge out even more samples as bogus, to clean it up further).
Yep, exactly. Samples marked as bogus are excluded from any calculation involving location data. That means Visit radius/centre calculations, Place radius/centre calculations, and also Trip item durations and distances. (So for example if a trip item had a patch of very messed up data along the way, you can mark it as bogus and the distance/duration calculations will skip over those samples, treating them as not existing).
Yep. So in theory if you only ever used the “clean up” feature, never doing any manual stationary/bogus cleanup, the Place radius would bias smaller over time. Although in practice it’s not enough of an effect to be a concern.
Aside: The “clean up” feature doesn’t quite do what it says it does. It uses the orange circle plus 2 standard deviations. Place and Visit radiuses are calculated as average sample distance from weighted centre, but then also stored alongside the standard deviation, to allow for different radiuses for different purposes. Like, some overlap tests work best with mean+1SD, some with mean+2SD, etc.
Place orange circles are actually mean+1SD, and “clean up” worked out best in testing with mean+3SD. Oh and Visit circles are mean+2SD. The different radiuses look intuitively more “correct” in the UI
In the next Arc update there’ll also be an option to mark entire items as bogus (with some caveats), instead of having to go into the individual segments of an item and mark each segment bogus. This makes it faster to clean up overnight drifts that broke out of the Visit’s gravity well and ended up becoming separate drifting timeline items.