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Fit file data from Garmin

bernardmcdonaldbernardmcdonald Posts: 42
edited September 2017 in Workshop
I am not sure if this is the correct part of the forum for this query or even if there is a correct part of the forum for it, but here goes.

I was recently involved in a collision and need to establish my speed and approximate rate of deceleration from about 5 seconds prior to contact until immediately afterward. I have video footage of the incident from a bar mounted go-pro and a fit file recording my ride on a Garmin Edge 800.

Can anybody help with suggestions as to how I can extract the speed data from my fit file? Any suggestions or assistance gratefully received.

Posts

  • I am not sure you have enough density of data point to work out something reliable on a 5 seconds timescale. It might come out with a aompletely meaningless number
  • I fear you're right. I tried playing with Golden Cheetah and exported the data. It tells me I went from 21mph to 15.4 mph in 4 seconds and then to 0mph in 1 second. I'm not optimistic.
  • imposter2.0imposter2.0 Posts: 10,839
    I have video footage of the incident from a bar mounted go-pro

    Leaving aside the Garmin data - if you have video footage, you should be able to establish your speed using fixed points in the footage as references..
  • slowbikeslowbike Posts: 8,476
    The Garmin will record positions at points - along with key data depending on your sensors - such as your power, heartrate, cadence. It can record every second or use (iirc) "Smart recording"
    https://support.garmin.com/faqSearch/en ... 3361847401

    It sounds like your device is using Smart Recording - therefore the data granularity you desire is not there. So it looks like you need to do some detailed analysis of the video and manual calculations.
  • Imposter wrote:
    I have video footage of the incident from a bar mounted go-pro

    Leaving aside the Garmin data - if you have video footage, you should be able to establish your speed using fixed points in the footage as references..

    I was always rubbish with a slide rule :(:(
  • slowbike wrote:
    The Garmin will record positions at points - along with key data depending on your sensors - such as your power, heartrate, cadence. It can record every second or use (iirc) "Smart recording"
    https://support.garmin.com/faqSearch/en ... 3361847401

    It sounds like your device is using Smart Recording - therefore the data granularity you desire is not there. So it looks like you need to do some detailed analysis of the video and manual calculations.

    It looks like you're right, but I had changed from the default and had it set to every second recording. Question now is this - is the every second data true or smoothed? Can I rely on the second by second speed recording.

    Also, it may be important that the speed was measured using a speed sensor and not from GPS.
  • imposter2.0imposter2.0 Posts: 10,839
    Imposter wrote:
    I have video footage of the incident from a bar mounted go-pro

    Leaving aside the Garmin data - if you have video footage, you should be able to establish your speed using fixed points in the footage as references..

    I was always rubbish with a slide rule :(:(

    Me too, but a) you won't need a slide rule and b) this may be your only option anyway. It's just the standard speed = distance/time equation, so assuming you can identify two or more fixed references in the footage, then you simply need to go back and measure the distances between them, and then start the timer..
  • It looks like you're right, but I had changed from the default and had it set to every second recording. Question now is this - is the every second data true or smoothed? Can I rely on the second by second speed recording.
    The recorded data is not smoothed. You should be able to rely on it.
  • davidofdavidof Posts: 2,018
    Use the Virb video software then you can overlay the speed data onto your video, you can probably slow the video down quite a bit too.
  • CiBCiB Posts: 6,098
    Data in a .fit file is in binary format and hard to get at, but if you sign up to RideWithGPS.com and upload your ride to it there's an export option which downloads the same data as xml, which is much easier to work with. From memory it's the Export As .tcx option.
  • If you are looking at using any data of this kind in court then you are going to need evidence from Garmin or whoever about how the data is recorded. There may be expert witness type people who would do the work for a fee. TRL used to do this sort of stuff.

    And as for using the video recordings, other than for very ballpark figures it opens up even more cans of worms.

    Good luck
  • apreadingapreading Posts: 4,534
    Try this: http://garmin.kiesewetter.nl/

    Convert to .CSV and open in Excel. Will show you all the data recorded. Speed is shown in metres per second so you will need to convert that if you want mph.
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