Display Delay

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csmarx
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20 or more Posts ★★★
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Joined: Wed Sep 07, 2011 11:30 am

Display Delay

Post by csmarx » Wed Sep 07, 2011 12:17 pm

I asked Harry the following:

In a GoPro video I can see the display of LapTimer in the windscreen.    I noticed that the live timing display of your app seems to be delayed by a couple of seconds. Is this normal?

The result is that when I do an overlay on the GoPro video that's correctly aligned with the start and finish, then the timing view displayed on your app in the video is not synchronized to the overlay timing in the video, but is off by a couple of seconds.

Another way to see this is that the live lap timing as seen by the GoPro camera starts and stops a significant distance after the start and stop respectively.

On this topic could you please explain the purpose of the new overlay synchronization in expert settings?

Also what is the function of the sensor delay settings?

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Here is Harry's answer:

The reason all display in LapTimer is behind reality is easy. You move with your car. Position calculated within the GPS chip is based on run time measurements from satellite signals from the past (maybe 0.5s?), calculation takes some time (maybe up to 0.1s?), update rate is 1Hz (which makes up to 1s), and display in LapTimer is done at a certain refresh rate too (10Hz, so again up to 0.1s delay). Adding this up means the position and speed displayed online is up to approximately 2s late (this improves with a 5Hz chip by 0.8s). Same its true for trigger detection. As LapTimer triggers when it detects the first position past the trigger, there is up to 1s in addition. So leads to late 'beeps' for trigger events and late start of the internal video. On the other hand it does not hurt timing accuracy as LapTimer uses the time stamp delivered from the GPS compensating any runtime impact. Furthermore you have the same situation for the stop position. The video by the way is one of the fastest in terms of gap between reality and display...

All the sensor delays in Expert Settings are for aligning the sensors with each other (acceleration, GPS, OBD, ...) - they all have there own timing behavior and do not even come attributed with a valid timestamp. For normal operation this can stay like it is. In case you see some severe discrepancy in recordings, you may adjust. The video synchronization is for overlaying only, it allows you to align the ends of video and the end of according a bit.

- Harry
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