How to know which sensor/device provided the data for a field?

I can see that FIT files from an activity contain detailed information about the sensors and the watch, but is there anything that tells you which sensor produced the data for a field?

For example, a "cadence" field could be produced by the watch itself, an HRM strap, or a Stryd footpod. How do we know which one was recorded? It appears that the watch has a hierarchy of sensors that it selects from if they provide the same data. Is the selection stored in the FIT file, or is it only found in the (undocumented?) watch software?

Thanks in advance for any advice.

0 Ben FIT over 1 year ago

The sensor information is stored in the FIT file but it is in an undocumented message.

I saw your post about the Stryd Duo. The Stryd CIQ apps and data fields write custom data to the FIT file using "developer data fields". Developer data is a way to for CIQ apps to write custom data into a FIT file. This is where Stryd's running dynamic that you see in the file and in Connect is coming from. Other than displaying the developer data in the graphs, none of the custom developer data is used within the Garmin ecosystem. Although, I am pretty sure that Stryd is using this data in their platform.

The only way that your Garmin wearable would use the data from a Stryd sensor is if the Stryd sensor was natively paired as a foot pod. In that scenario the Stryd sensor, connected as a foot pod, would be used for pace and distance, and maybe cadence.

0 1148788 over 1 year ago in reply to Ben FIT

HI Ben, thanks for your reply. I think that what you say was correct until very recently when it appears that Garmin has allowed Stryd (the company) to interface with its internal running dynamics processing. The newly released Stryd Duo, when paired as a RD Pod, generates fields with the same names as those from the Garmin HRM Pro (e.g., "stance_time", "stance_time_balance"), and in my testing (e.g., looking at the statistical properties of the data) it strongly appears that these take precedence over the HRM Pro if both devices are present. It could be that the HRM Pro is then ignored entirely and the heart rate subsequently comes from the watch, I don't know.

Perhaps what decides the precedence is the order in which the devices are detected by Ant+ when an activity is initiated. Given that it is pretty elementary to know which sensor produced which data, it would be nice if Garmin could explain what is going on, and ideally open up the undocumented message that links fields with sensors. From looking at the Stryd Facebook page, it appears that the Stryd engineers are also in the dark.