Question about "Storage Rate" setting

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aMacUzr
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Question about "Storage Rate" setting

Post by aMacUzr »

Did a quick search and didn't see any discussion about this ...

For the "Storage Rate" setting, the blurb warns "Do not use 20 Hz except when driving short tracks only."

- what length constitutes a "short track" (or, more importantly, a NOT short track)

- what about when one's using an older 20 Hz VBOX for GPS and the "Storage Rate" is set to "GPS Rate"

- what would be the underlying limitation, why, and what effects would it have if 20 Hz is used and the track is "too long"

I'd prefer to use a set rate (and I use a 20 Hz VBOX, so that'd need to be 20 Hz). My thinking is that, by setting a fixed rate, when there's a GPS dropout (where, presumably, the rate also drops) the data-stored rate wouldn't be dependent upon the GPS rate and thus should not lose accel/ODB data because the GPS rate dropeed (... or is there something wrong with my black-box analysis of how things work).
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Harry
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Re: Question about "Storage Rate" setting

Post by Harry »

Hello,

This is just a warning to not overdo it. There is no hard limit and LapTimer can handle 20 Hz recordings even for tracks like the 20km Nordschleife. However, charts / maps get a bit slow when running it on dated smartphones. Furthermore, it makes little sense to interpolate eg a 1 Hz GPS signal to 20 Hz.

10 Hz is usually good enough to do all analysis.

For a VBOX Sport doing 20 Hz I recommend to use GPS rate. The effect of running 20 Hz storage rate on a 20 Hz input stream is quite heavy interpolation processing. It is true that a GPS drop of a max of 4s will be mitigated by this in theory, but I have never tested this or designed it to address such a situation.

Fixed storage rates have been introduced to allow storing IMU and OBD data coming in at higher rates even for the internal GPS running at 1 Hz. The second use case it to increase the rate slightly by eg setting 5Hz for 1Hz GPS.

Harry
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aMacUzr
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Re: Question about "Storage Rate" setting

Post by aMacUzr »

Thanks for the (as usual) thorough explanation.

Since I'm using an iPhone 6 for LapTimer data-only capture (video tracks are all externally captured on other devices), I'll set a 20 Hz rate and not worry about it.
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