[FAQ] Adjusting Calibration 'after the fact'

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Harry
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[FAQ] Adjusting Calibration 'after the fact'

Postby Harry » Sat Mar 19, 2011 9:08 am

Sometimes the acceleration calibration has not been adjusted correctly. On a straight accelerating, the acceleration indicator (either in Acceleration View or Video View) should be slightly south, not left or right, standing still is should be centered. This sometimes happens when LapTimer does not calibrate correctly - or when you press the calibration button to fast after turning the device to landscape / video.

LapTimer can calculate acceleration information from GPS. This is generally less accurate than measured values but better than acceleration recorded with wrong calibration. Goto Lap Details and press the Recalculate button in the bottom. Afterwards, if you had a video recorded, re-assign the original video (without overlay), and overlay again.

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Re: Adjusting Calibration 'after the fact'

Postby Singe » Mon Apr 23, 2012 2:44 pm

In v15.x there was no calibration or 'force calibration' that I could find. The linear and lateral acceleration numbers are not valid from my weekend sessions. When I use the Recalculate feature they still are not valid. So in v14.x the traction circle had valid acceleration data and so far I'm finding in v15.x it does not.

How does one insure that the measurements for linear and lateral acceleration will be valid in v15.x? Since the data is not valid for my last weekend is there any way the Overlay can omit the traction circle and show video with the lap time? Thank you.


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Re: Adjusting Calibration 'after the fact'

Postby Harry » Mon Apr 23, 2012 3:12 pm

You may navigate to the Acceleration view at any time. It shows the current values and includes the assistant as a hover view (touch the circle). 'Recalculate' has changed a bit in v15. Pressing 'Recalculate' allows selection of 'Acceleration' or 'Accuracy' now. Select 'Acceleration' and it will replace your measured acceleration values by calculated values. Take care you confirm every step (4 overall). Once acceleration has been recalculated, apply a new overlay to the raw video and it should show the calculated data.

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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby francesco » Wed Jan 23, 2013 10:36 am

Don't know if this is a bug but I thought I should post this.
The acceleration callibration was fine during my recording, but after a Agenda item popup the callibration was off. See attachment.

I don't know if this is normal or if this a bug. A suggestion is to recalibrate during the session? Will the overlay from the first part of the session still be available? Is it possible to recalibrate during a session/recording?
Attachments
foto.jpg
foto.jpg (23.88 KiB) Viewed 4790 times


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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby Harry » Wed Jan 23, 2013 11:13 am

It is not possible to recalibrate while driving. LapTimer checks for the car standing still pretty early in the process - which is never the case on track. While standing still, LapTimer eliminates the gravity vector and a potential tilt of the iPhone. Once you are back in the pits you can easily trigger recalibration by tapping into the acceleration circle above. For laps you have recorded with "wrong calibration", check the posts above - you can recalculate them.

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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby francesco » Wed Jan 23, 2013 1:14 pm

Thank you, it is clear how to solve the problem after it occurs. Would be better to prevent this from happening, I will check my agenda items before I will go to track :)


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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby Nizzle » Thu Apr 18, 2013 7:14 pm

I used laptimer for the first time this past weekend's autocross. Working on compiling my videos so I can share with my codriver.

I have a couple runs where it looks like the accelerometer was calibrated correctly and some where it looks all wrong.

Here's a good one:
Image
Image
Image

and a bad one:
Image
Image
Image

LapTimer has three options when I go to recalculate.
"Splits", "Acceleration", and "Accuracy"
which one should I use and why? "Acceleration", like you said above, corrects based on the GPS data, so my acceleration data for the bad run will be @ 1Hz in line w/the GPS, correct? "Accuracy is to recalculate for the GPS, correct? Can you revert to the original values if for some reason, you don't want the recalculated results?

Is there a way of getting LapTimer to lock just one calibration setting? I have my phone securely locked onto the top of the roll bar. Once it's there, I don't want it to change calibration settings even if I disconnect my phone from the mount (quick disconnect).

Truthfully, I didn't move the phone at all over the course of our last 3 runs. Yet, every time I looked at the video screen, the dot in the acceleration circle was askew ever so slightly. I had to tap the acceleration circle to get it to "recalibrate" and even by doing that each time, 3/5 recorded runs gave funky data.

Thanks!


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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby Harry » Thu Apr 18, 2013 9:42 pm

Acceleration recalculates longitudinal and lateral acceleration based on GPS. There is no way to revert to measured data - except by exporting the lap data to .hlptrl to have a backup. Accuracy is for external GPSes only (actually an Expert function that should not be ran except when advised).

Please note LapTimer stores *all* data aligned to GPS. So although acceleration data is sampled at a higher rate, LapTimer stores only 1 fix aligned to the GPS fix per second. The aligned value is the max value detected half a second before and behind the GPS fix. Autocross is difficult in this respect as it has rapid direction changes actually requiring a much higher recording rate than 1 Hz. So in case you are serious about acceleration, a higher rate GPS is recommended.

There is no option to lock calibration as the overall mechanism is planned to be replaced in a future release.

- Harry


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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby Nizzle » Thu Apr 18, 2013 10:49 pm

Autocross is difficult in this respect as it has rapid direction changes actually requiring a much higher recording rate than 1 Hz. So in case you are serious about acceleration, a higher rate GPS is recommended.


Will the Dual XGPS 150 Bluetooth GPS Tranciever work good for AX? My plan was to use that as my phone case (Hitcase Pro), while rugged, eliminates the use of the iphone 30-pin port. Please don't burt my bubble! :?

Any ideas as to why Recal of the accelerometer didn't work 100%?


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Re: [FAQ] Adjusting Calibration 'after the fact'

Postby Harry » Fri Apr 19, 2013 3:08 pm

Yes, the Dual will give you much better values here. On recalibration: usually LapTimer keeps a calibration achieved. There are certain situations however, things are reset. LapTimer runs a sanity check calibration is fine from time to time. If e.g. LapTimer detects zero speed, but a high acceleration (actually it should be zero), it will start over automatically.

- Harry


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