Speed is delayed

Help on issues you run into with LapTimer; in case you have a question on how to use LapTimer, use the forum "Using LapTimer" instead
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MagnusMJ
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Speed is delayed

Post by MagnusMJ » Fri Jun 05, 2020 3:14 pm

When I overlay my video, everything seems right, but the speed is way ahead. The g-force seems to be right, and the point where
the laptime is collected also seems right, but the speed seems to be a second or so ahead.
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Harry
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Re: Speed is delayed

Post by Harry » Fri Jun 05, 2020 6:19 pm

Solving this depends a bit on which speed is displayed... In case you use an OBD adapter, wheel speed is used, otherwise GPS speed is used. Usually GPS speed is *behind* positions reported, not vice versa. As you will not see slightly wrong positions, speed is the significant value when adjusting sync. In case acceleration is o.k., you will need to decrease the GPS sensor delay a bit for you next recordings. For existing recordings, shifting GPS against acceleration is not supported. The only thing you can do is shifting data against video frames completely. Instructions on this can be found in this FAQ: viewtopic.php?f=39&t=4940

Please note this is a complex topic. Search for "sensor delay" here on the forum to see discussions we had over the years.

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Re: Speed is delayed

Post by MagnusMJ » Sat Jun 06, 2020 11:44 am

I'm using using GPS from my OnePlus phone.
But I'm not sure my calibration is done right.
I've mounted the phone I the bottom right corner of the windshield of my Lotus Elise, and is mounted horizontally. I haven't done any calibration, I just used the preset.
Here is an example of how the speed is shown.
https://youtu.be/lRjmnUp666o
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Re: Speed is delayed

Post by Harry » Sat Jun 06, 2020 11:52 am

To me it looks like the position is in sync while speed is *late*. The reason might be that speed is heavily smoothed by your OnePlus, thus adding the lag in display. To find out, please select the lap from Lap List and follow Data Recordings ‣ Preview. Switch to the Charts tab. You will see the speed diagram now and can check speed development:

Provided you have LapTimer GP, tap a position showing a minimum speed. This will be in a corner. In case this position shown in the map gadget does not match the slowest point, there is a speed shift in raw data - i.e. the one LapTimer received from your OnePlus. For Petrolhead, you can zoom into the speed curve and get the respective section shown in the map gadget.

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MagnusMJ
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Re: Speed is delayed

Post by MagnusMJ » Sat Jun 06, 2020 3:00 pm

When I tap the minimum speed in the corner after the straight, it says time: 00:11:64, but on the picture shown with the overlay on, it says 00:15:30
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Re: Speed is delayed

Post by MagnusMJ » Sat Jun 06, 2020 3:02 pm

Here is a screenshot
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MagnusMJ
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Re: Speed is delayed

Post by MagnusMJ » Sat Jun 06, 2020 3:06 pm

Here's is another lap I haven't overlaid yet
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Re: Speed is delayed

Post by Harry » Sat Jun 06, 2020 3:09 pm

Well, I don't know where the lowest speed for this corner will typically be, but the data looks sound to me? But the position in the video frame is later than the one in the map gadget. So it is well possible there is simply misalignment between data and video. Please have a look into this FAQ: viewtopic.php?f=39&t=4940

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Re: Speed is delayed

Post by MagnusMJ » Sun Jun 07, 2020 12:37 am

If I time the video with the speed, the g-force is completely off
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Re: Speed is delayed

Post by Harry » Sun Jun 07, 2020 7:57 am

This means GPS and acceleration are not in sync. You can‘t change this after the fact (like the video sync) because these values are fused during recording. In case this occurs regularly, ie the sensors are out of sync in general, sensor delays need to be adjusted. If eg acceleration is ahead, you need to decrease the acceleration delay (or increase GPS). These values will be applied starting with your next recording.

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