GPS time comes back in with +12 hours to it from actual capture

[threehan]

Hi!

I'm not sure if it is bad data or if I'm using the tool wrong. I have a dashcam video that was created at 11:35 am and my gps timestamps are showing 23:35Z. For what its worth, the video clearly shows 11:35 on the burn in. Here is the -v3 dump from the last gps coordinate. Any help would be appreciated

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+ [GPS directory, 16384 bytes]
  |  d8ded8c: 00 00 40 00 66 72 65 65 47 50 53 20 f0 03 00 00 [..@.freeGPS ....]
  |  d8ded9c: 17 00 00 00 23 00 00 00 2a 00 00 00 41 00 00 00 [....#...*...A...]
  |  d8dedac: 46 ce c2 9e 66 e8 a6 40 4e 00 00 00 00 00 00 00 [F...f..@N.......]
  |  d8dedbc: f6 7f 0e f3 6d 3a c3 40 57 00 00 00 00 00 00 00 [....m:.@W.......]
  |  d8dedcc: 42 60 e5 d0 22 5b 3c 40 b8 1e 85 eb 51 88 69 40 [B`.."[<@....Q.i@]
  |     [snip 16304 bytes]
  | GPSDateTime = 2023:01:17 23:35:42Z
  | GPSLatitude = 29.5366738333333
  | GPSLongitude = -98.7476496666667
  | GPSSpeed = 52.515312
  | GPSTrack = 204.26
  | Accelerometer = 1.074 -0.283 -0.64

[StarGeek]

What is your time zone?  GPS time stamps are supposed to be set to UTC.

[threehan]

I'm central standard. The video was recorded in the cst time zone as well.

[Phil Harvey]

Central standard time is UTC-6.  So are you saying the times are 6 hours out then?:

was created at 11:35 am and my gps timestamps are showing 23:35Z.

Can you upload a video somewhere so we can take a look?

- Phil

[threehan]

Here is a Google drive link. Thanks for taking a look

https://drive.google.com/file/d/1cDwoji3OImwfdWvNaD8nUPc0UM6wiUd8/view?usp=drivesdk

[Phil Harvey]

OK, this is rather straightforward since your device stores an NMEA RMC sentence, which has a well-defined syntax.  The first point stored in the file you uploaded has this NMEA RMC raw data:

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$GNRMC,233242.000,A,2931.52494,N,09843.04091,W,0.000,272.01,170123,,,A*59
the syntax for the RMC sentence is:

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$GxRMC,hhmmss.sss,A/V,ddmm.mmmm,N/S,dddmm.mmmm,E/W,spd(knots),dir(deg),DDMMYY,,*cs
from which ExifTool (properly) decodes the time as:

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GPSDateTime = 2023:01:17 23:32:42Z
(Z = Zulu because NMEA RMC stores UTC time.)

The first timestamp burned into the video is

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01/17/2023 11:32:41
Which makes it clear that the video was recorded on a system where the time zone was set to -12:00 (ie. your dashcam settings).  Since this isn't your time zone, I suggest that you correctly configure the settings of your dashcam.

- Phil