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Comment by zknill | Hacker News Reader

GPS traces recorded on a watch can be pretty noisy. If you stand in the same spot for a while, you're not going to get the exact GPS position recorded for the entire time you're there. The same happens when you move, it's not a smooth trace.

Strava (and I assume to some extent Garmin) apply some smoothing to these raw GPX traces to try and improve the path, or remove some of the noise.

You'd be missing out on this post-processing by taking the data raw. Ofc you can implement something similar yourself, but I wanted to point out that these platforms are doing a little bit more than just displaying the GPX trace.

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When parsing high end Garmin and Apple fit files, it appears a lot of their smoothing is done before writing to the fit file. They’re in a very workable state straight out of the gate.

Yes. The location data you get from CoreLocation has been processed already, in that it is the output of combining the inputs from the GPS, Wi-Fi access points, cell towers, magnetometer, accelerometer, and gyroscope sensors.

Workout data might take it a step further, as you tell it the type of workout, and I'm assuming WorkoutKit might do something like adjust the distance filter that specifies how far the device has to travel before triggering a location update event to minimize battery use during the workout.

https://stories.strava.com/articles/explaining-the-strava-ta...

Interesting article (which I think is relevant)

But how real of a problem that is?

I wander often on many smartwatch/sport tracking forums/subreddits, and it's fairly frequent that people ask how to deal with smoothing and get back raw data. Some love how Garmin smooths out a race track run for them and make gps trail stick perfectly to a lane. Some pull their hair out seeing their lake run being smoothed out to make it look like they jumped over fences and private properties.

I often find my garmin traces confusing as well, it's not objectively better.

Some users may be confused about Garmin functionality. If you select the Track Run activity profile on a standard 400m track then it will generate a perfectly smooth and consistent route every time. This is only possible because it knows the exact shape of a standard track and can adjust the location data points to fit.

All fitness trackers (and mobile devices in general) do some level of smoothing on location data before recording it to an activity. There is no "raw data" to get back. The developers try to select smoothing algorithms that produce a good result in most cases but there will always be occasional discrepancies. This is usually due to poor signal quality including multipath reflections when the device doesn't have a clear line of sight to the sky due to structures or trees.

Garmin devices don't only use "GPS". They support multiple GNSS constellations including Glonass and Galileo, and depending on the selected mode may use all of those simultaneously to improve location accuracy.

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