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Discrepancy between accelerometer and gyroscope data

AlmogAlmog
in General
Hi!

I used the metabase app in order to log data from metamotionT sensors. I noticed a time stamp discrepancy between accelerometer and gyroscope data - the time stamps are different between the different CSV files. The difference varies between about 20-1 milliseconds. I used 20 different sensors and the problem exists across all of them.  

Unfortunately I conducted a lot of data before I noticed this problem and I'm in the process of figuring out the ramifications of it. Is this a known problem? Can I fix it retroactively? Is there a method to prevent is in the future?

Comments

  • EricEric
    You can align the two files by simply pairing the data from the latest start time to earliest end time, discard the other data.
  • AlmogAlmog
    Thanks. I found some bigger discrepancies of about 8 second. Can you please give me an example for the pairing so I'll be sure I understand?  
  • EricEric
    Check out this tutorial on our web page:
    https://mbientlab.com/docs/data-analysis/data/syncing-data-from-multiple-metasensors/
  • AlmogAlmog
    I read the tutorial, but I'm afraid it doesn't exactly cover my case. My question is - can I trust the time stamp? 
    As described, I sampled using one metamotionR sensor and activated accelerometer and gyroscope (100Hz). I expected to see identical time stamps for both but it wasn't. 
  • EricEric
    edited September 2017
    The firmware does not treat acc and gyro data as one sample and MetaBase starts them in series.  They do share the same clock in the hardware thus my suggestion of pairing based on latest start time and earliest end time.

    The timestamps will never be exactly aligned however you should be more concerned with the relative time offsets and number of samples received.
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