Timezone for this Ambit 3 file

Pascal 3 months ago

Hello,

My understanding:

Timestamps in Garmin FIT are in UTC. If there is a local timestamp in the activity message, you can make the difference between local timestamp and timestamp to know the actual time.

If this message is not present, you have to check the GPS coordinate to know the timezone, daylight saving etc.

In the attached file, at least from fitparse libray, I see that there is a local timestamp in the activity message. But this local timestamp is showing 0 difference which would mean that the "real" time is the UTC time which it is not. Departure time is 9:18:42 and not 7:18:42

Yet fitfileviewer.com correctly display the departure time at 9:18:42 so I may miss something or maybe the best pratice is not to check the local time but to get the UTC and transform to real time by checking the timezone with GPS coordinates.

Any experience?

Benoit-SuuntoAmbit3Cycling_2024-08-02T09_18_42.zip

thanks

0 muktihari 3 months ago

Yes correct, the only thing that you miss probably this:

fitfileviewer.com shows time based on location you open the website, in my laptop it shows 2:18:42 PM, since my current location is at GMT+7. Please toggle the Developer Mode on to show the timestamp in uint32 value, then you can use https://developer.garmin.com/fit/cookbook/datetime to convert the value to time.

The timestamp in uint32 value is 1091517522, equivalent to Fri, 02 Aug 2024 07:18:42 GMT.

If the device is yours, consider setting the timezone to avoid the current issue from happening again, this might help: https://www.suunto.com/en-id/Support/faq-articles/lifecycle/how-do-i-change-the-time-of-my-suunto-watch/

If you are only the consumers of the files, you can still determine the timezone using GPS coordinate when you can't get the timezone by extracting it from local timestamp. These 3rd party libraries might help:

1. https://github.com/bradfitz/latlong (Go)

2. https://github.com/evansiroky/timezone-boundary-builder?tab=readme-ov-file#lookup-libraries (Multiple languages)

0 Pascal 3 months ago in reply to muktihari

Ok but my suprise is that there is a "local timestamp" in the activity message, so it should indicate me the timezone. If there was no local timestamp, it would be ok....but here it seems weird: there is one but it is not correct.
It doesn't seem to respect the FIT standard

0 muktihari 3 months ago in reply to Pascal

The question is, if the watch's time setting is (mis)configured in UTC, should the local timestamp field be omitted?

0 Pascal 3 months ago in reply to muktihari

I will ask the owner of the watch

0 Pascal 3 months ago in reply to muktihari

This watch time seems well set… yet by looking on other forums, seems to be a known/recurrent problem on this watch…so probably not following well fit standard

0 muktihari 3 months ago in reply to Pascal

I see, it seems a bug then, need to ask suunto for the firmware patch.