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Silly question. GPS and time.

Discussion in 'General Discussion' started by Narrator, Jan 6, 2015.

  1. Narrator

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    I have been wondering where the camera in my V+ gets its time stamps from.
    Then it occurred to me, it probably comes from the GPS data.
    Would this be true?
     
  2. Hughie

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    It is certainly availble in the GPS data - so I assume so.

    https://en.wikipedia.org/wiki/Global_Po ... imekeeping
     
  3. Prylar Bek

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    What do yo mean? Like recording time? Mine doesn't 'stamp' as much as just shows recording time, until I xfer it to the comp, then it stamps it> Is that what you mean?
     
  4. Morgon

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    Huh? He's asking how the file's creation time is generated on the filesystem when the images/videos are saved.
     
  5. Prylar Bek

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  6. Narrator

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  7. N017RW

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    First let me say I don't have a V+.

    But are you sure you're not talking about the file's time/date/etc when you up load to your PC?
    That has nothing to do with GPS data from your a/c.
     
  8. Narrator

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    Yep.. I'm sure.
    The file time stamps match the time of recording, not the time of uploading to the pc. Also, the uploading takes only a couple of minutes, but each file is stamped as being about 20 min apart - the life of each battery.
     
  9. N017RW

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    The GPS clock is UTC I beleive thus requiring some addtional input (offset) to convert to your local time.

    My guess is it (the Naza) is sync'ed with your PC clock during upgrades, calibrations, etc.

    Curious to see what others may think.
     
  10. Narrator

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    I read Wikipedia regarding GPS. It said something like this: The receiver must get 4 GPS signals, from which it calculates the actual time, based on angles and time stamps from the satellite telemetry. (Something like that anyway.) :p
     
  11. N017RW

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    Separate issue.

    True, GPS is time based.

    However local time is irrelevant to positioning.
     
  12. Narrator

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    Tell me if I'm reading this wrong.

    http://en.wikipedia.org/wiki/Global_Positioning_System#Non-navigation_applications

     
  13. ianwood

    ianwood Taco Wrangler
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    GPS systems broadcast UTC time. They also broadcast their position. The combination of the two can be used to determine how far you are from the satellite which combined with other satellites can determine your location (oversimplified).

    GPS signals do not help with determining what UTC offset applies to your location or if any daylight savings functions are in place. Therefore they will need ground based information to determine the local time.

    That ground based information could be held in the Naza firmware as it doesn't change often. Make all this information available to the controller that writes files to the SD card, it should be able to apply a localized date and time stamp.
     
  14. PhantomFanatic

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    Yes, it is included with GPS data, as was stated earlier.
     
  15. ianwood

    ianwood Taco Wrangler
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    Local time is not included with GPS data.
     
  16. Narrator

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    From the same page I linked earlier:

     
  17. Hughie

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    I assume that the UTC time is derived from GPS. What other options are there.

    This really is a question about where does the Phantom get its timezone info from. This could be done as has been suggested based on the PC clock that the assistant is on. I would be interested to see if in addition to timezone, the daylight savings time (DST) profile is taken account of. These can be fiddly to apply on an international product. Even where DST is defined it can still have exceptions. For example Arizona I believe has regions which do their own thing.

    Great question - not silly.
     
  18. N017RW

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    GPS to UTC offset is different than the offset for UTC to local time.
     
  19. Hughie

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    Yes a completely different beast. All this needs doing :

    GPS ->UTC (using GPS offset)
    UTC->Local (using timezone)
    Local->Wallclock time (using daylight savings for local region)
     
  20. ianwood

    ianwood Taco Wrangler
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    More easily and accurately implemented in Naza firmware using very simple business logic and polygons as has been done with no fly zones.