Lap time vs. lap end time

[bldn10]

On the Laptimer Integration page for a lap I noticed that it says the lap ends at 1:41.14 but the recorded lap time is 1:42.41. When I scroll through the video it does look like the finish line is closer to 1:41.14. What gives?

[Harry]

Video recording typically starts late (latency between trigger event and camera "warm up"). This means you will typically miss the first 1 or 2 seconds of the lap on video. A similar difference occurs for the end of the video - the event for the end of track is coming in late (GPS is always late by 1 or 2 seconds), so video is stopped a little late too. Overall this means, no stream of data (GPS / video / etc) will ever match exactly 0 and the lap time. LapTimer tries to calculate the best offset from the video start (thats the number shown in LapTimer Integration) that match the "real" end of lap.

So no worries, it is complex and confusing, but LapTimer takes care.

- Harry

[bldn10]

This is true even for successive laps? I.e. the camera is running nonstop and never starts or stops. So which time is the accurate one? I assume the start and stop delays cancel each other out? So, essentially the finish line is moved back the distance = to the delay?

Too complicated for me!

[Harry]

The late triggering due to the fact GPS is always delivered late is the same for each lap - or for each trigger. Not sure you really want to go into this discussion - we had it several times on the forum already. In short: when a new GPS position is received, it is around 1 to 2 seconds old. This is due to the time for the signal to travel, processing times etc. As this GPS position comes with the original time stamp (satellite time / atomic clock), LapTimer can compensate any latency for timing calculation. The cam however is triggered late because it can be triggered when the signal arrives in real time - i.e. late. So the video timeline is kind of "shifted" compared to "reality" (taking GPS time as the reality). LapTimer has adjustable delay setting for all sensors to map a real time event back to GPS time. This is necessary because only GPS has a atomic time stamp - all others (including OBD) are less accurate.

So no worries, it is complex and confusing, but LapTimer takes care.

- Harry