Wrong Altitude on Track Recordings

Hi all,

I’ve recorded several tracks recently which show wrong altitudes (e.g. going to -24m for several seconds while not changing altitude at all; see attachments).

I’m pretty sure it’s not Trails fault but am still wondering where this issue can come from.

I’m on an iPhone X with iOS 11.3.1.

Anybody any idea?


Hi Daniel,

this is a known issue and while we’re investigating this issue (and have been for a while), we do not have a solution yet.

Our observation is that this issue is worse on recent phones (iPhone 7 and later) and recent versions of iOS (10 and later), but we cannot reproduce it on demand.

Generally, Trails relies heavily on the GPS signal. We try to detect/filter obvious jumps, but it’s not trivial to tell actual movements from these errors automatically. We have a couple of sample recordings with this issue and the recording accuracy (as reported by the GPS) isn’t significantly different in spots that the human eye easily detects as inaccuracies.

Thanks for your reply!

Please let me know if I can help somehow. The effect you’re describing appears in all my recordings.


I have the same issue with my iPhone 8. And also calculation of the ascend and descend is wrong.
Maybe the integration of the barometer in a “altitude filter” in the GPS measured altitude could improve the accuracy.