As I understand it, the GPS timestamp field is a time-only field in EXIF data converted to the UTC timezone, but I'm looking for clarification around where it's value comes from.
I understand the rest of the image's timestamps come directly from the device's internal clock, but the time value in the GPS data doesn't appear to be consistent with them (when adjusted to the correct timezone, of course).
I also realise that the iPhone caches location data in consolidated.db.
My example I have two photos taken (on an iPhone 4) within 20 seconds of each other. All other timestamp fields match up correctly.
The first image has a GPS time that comes out as 34 mins later than the image's timestamp.
The second image however comes out as 50 mins earlier than its other timestamps!
The coordinates are exactly the same, so if it was a matter of the device grabbing a timestamp from consolidated.db, I would expect them to be the same, or at least the second being later than the first? Or could the row retrieval from consolidated.db be more random, or perhaps kicking off some other location data update process?
Any information you could provide would be great!
Did you look here? http//
There are options to consider regarding the source of GPS data fed to the EXIF embedded in the images.
Is the GPS data from the internal GPS hardware which imports directly to EXIF?
From an external GPS module (eg GPSSerial etc)?
A commercial SDK Dev app that is importing the GPS data to Exif?
Is it A-GPS which pulls data from the internet?
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Apple suggests location data refreshes every several seconds and stored older refreshes aggregated up to 15 seconds old are discarded.
But then Apple also suggests location data refreshing in iPhone is a battery resource greedy operation so the refresh of GPS data may need to be diluted unless accuracy is paramount.