Question on FIT file parsing: Misaligned Splits / "Summary First" vs "Summary Last" handling

[Jaap_van_Ekris]

@R2Tom

And what does your speed stream look like? Because if your average speed in this interval would be 200m/min - then what would be correct? Distance or speed?

Good question. In indoor rowing, I’d go for distance. In essence, we know two things certain: time and angular displacement of the flywheel. Via dragfactor (which is calculated on the recovery) we can easily get to distance travelled. In OpenRowingMonitor and the Concept2, these are continuous metrics: time and distance are continuously updated (ORM updates it once per pulse, about 2 - 5 ms).

As instantanuous velocity varies quite a bit across the stroke, we can only calculate pace across an entire completed stroke. Here small stroke detection errors influence average pace. Not large changes, but sufficient to be noticed.

This nature of velocity calculation in rowing (indoor and outdoor) would result in total nonsense results if extrapolated (or interpolated incorrectly). Extrapolation based on last reported speed goes wrong as the speed is a lagging indicator (usually one to two strokes) and we start by accelerating the flywheel/boat to its maximum speed. So any projection over a short distance actually misses the mark (unless working on instantanuous speed over a short distance). Any extrapolation on average pace is doomed. Concept2 actually rounds its projections of finish time to whole seconds to work around this.

This gets worse if you use time-based reporting, like Garmin does, as you then become totally clueless what the starting point of your pace reference becomes. It could be that you are extrapolating just after the large acceleration that is the drive (for reference, a 2:00/500meter pace typically consists of a stroke of 1 second at 600W, followed by 2 seconds of recovery at 0 W) so the distance already includes this.

@R2Tom

As intervals was a cycling platform at first, I think it consider speed as more trustable (because on a bike a speed sensor is more reliable than GPS distance).

That makes sense for a historical perspective indeed.

Mentally, compare this with an old-school bike computer where the computer measures wheel rotations. Rowing is a bit more compkex than that, but in essence from a metrics reliability, it captures how we are measuring.

@R2Tom

Of course this shouldn’t be the case for indoor rowing. But anyway, if speed /time is different than distance, which one would you trust more? And can you confirm, that your speed stream is accurate?

In ORM, we base speed on distance travelled over time, so it is accurate across a completed stroke. Within a stroke, it isn’t accurate as it is an average where we start with a considerable acceleration. So time and distance can be trusted, speed isn’t.