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Time in GPX goes back!!

45XL_iQue3600_Nuvi3490
This is my first question on this forum. Since 1996 I'm using Garmins, first a 45XL, then an iQue 3600, and from 2012 a Nüvi 3490LMT.

As you probably will know, the Nüvi saves all its tracks in gpx-files. I read these tracks in my database application. Sometimes (more precisely 3 times, all of them in the last 5 months) my database crashes
while reading the GPX, because of some rare case: the time goes back!

I give you an example. The time in the fourth record is 1:56 earlier than in the preceding record, 15:16:17 vs. 15:18:13. Because of this I guess, the gpx gives no speed info in the 15:18:13 record.

<trkpt lat= ... ><ele>-15.24</ele><time>2016-02-23T15:17:57Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:speed>12.35</gpxtpx:speed><gpxtpx:course>261.18< ...
<trkpt lat= ... ><ele>-14.76</ele><time>2016-02-23T15:18:06Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:speed>4.12</gpxtpx:speed><gpxtpx:course>268.24< ...
<trkpt lat= ... ><ele>-14.28</ele><time>2016-02-23T15:18:13Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:course>269.65< ...
<trkpt lat= ... ><ele>-12.84</ele><time>2016-02-23T15:16:17Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:speed>8.24</gpxtpx:speed><gpxtpx:course>272.47< ...
<trkpt lat= ... ><ele>-12.84</ele><time>2016-02-23T15:16:25Z</time><extensions><gpxtpx:TrackPointExtension><gpxtpx:speed>13.73</gpxtpx:speed><gpxtpx:course>282.35< ...

What's happening here? Is it my Nüvi's internal clock?

Thanks!
  • 0
    No, it is not your device's clock. Time on your device is corrected based on the position calculation (meter gps accuracy requires time accuracy on the order of 10^-9 seconds). My guess would be that it is a buffering error. Perhaps your device reached the end of the current log and either was starting over or archiving the filled log. Maybe it occurs when satellites leave and enter a devices field of view.

    This sort of thing has happened on other devices and usually is corrected in a firmware update. Be sure to report this to Garmin so that they are aware of the problem.

    As you are probably aware, there will be a section of duplicated data (the earlier time stamps) that will have to be deleted from the gpx file in order for it to be read.