Hi,
Since October 2022 I’ve a Pixel Watch and since January I encountered a measurement bug. I’m not complaining about a slightly inaccuracy between the total distance and distance displayed in the pace view. Even on the Fitbit Sense I owned before the total could differ by 10 meters per km I ran.
My reported issue is, that the Fixbit app stops to accumulate the distance for 300 – 600 meters (1.5 - 3 minutes), although the GPS data points in the tcx file differ for every second within the ignored distance. The total distance in the app and the number of expected steps is correct, but the run distance in the pace table is missing the skipped distance and the pace for the km where the app stopped to accumulate the distance is worse, because related to the recorded time and the corresponding distance to complete the next km, I needed more minutes. But actually I didn’t slow down and speed up again.
I don’t think that this is a hardware issue, because when I uninstall the installed version of the Fitbit app and I use the original installed version which is a part of the Pixel Watch Android version, I can’t observe, that the GPS points change, but the distance remains constant. Of course, when the GPS signal is weak then the distance is incorrect, but in this case also the GPS points are incorrect, too.
I coded a small program which imports tcx files and calculates the distance and compares it to the accumulated distance. I used the algorithm posted here: https://stackoverflow.com/questions/365826/calculate-distance-between-2-gps-coordinates
I observed some differences between the version installed on the Pixel Watch Android OS and all the 2023 updates.
• The calculated distance between each two GPS points is almost the same, like in a tcx file recorded with the Android OS version of the Fitbit app. The marginal differences can be ignored.
• The updates from 2023 use a smoothing algorithm, I think to reduce effects from zig-zag which occurs, when the GPS signal is weak. The same smoothing I observed in the tcx files recorded with my Fitbit Sense.
To summarize:
- The issue only occurs in Fitbit app versions, which are newer then the version which is a part of Pixel Watch Android OS
- The issue occurs usually in one of 3-4 runs. Often after the third km, but sometime also with the first two km.
- There is no correlation between my location and the occurrence. It also occurs outside the town in the middle of nowhere. Without building or bridges which can shield the GPS signal.
- The totals displayed after the run on the watch are correct. This includes: The distance in km, average pace, number of steps and the total time.
- In the Android & IPad Fitbit App and over the fitbit.com web front end, the data is partially corrupted:
- Total distance and time are correct
- Average pace is incorrect, it is the ratio between distance without the missing meters and the overall time.
- Intermediate km displayed on the map are incorrect, the km where the issue occurs is longer then it was. Therefore the last intermediate marker is almost next to the final marker which is correct.
- The pace is incorrect for the km where the issue occurred
- The distance for the last km in the pace table is shorter
In the Fitbit forum I found other persons, who have the same issue. I think the algorithm which is used to smooth the GPS data points, has a bug. The issue also affects persons which uses the imperial measurement system.
For me it isn’t clear where the issue actually happens. It can happen during my run, in the preparation for the upload, during the upload or on the Fitbit servers.
If you want, I can provide tcx files, which includes sections which have changing GPS data points, but a >300m constant distance.
Regards,
Mapohb
