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RGlowitz
Participant
October 31, 2018
Question

Map module-track offset

  • October 31, 2018
  • 1 reply
  • 464 views

When traveling I make sure that my camera date and time match the date and time on my GPS which is set to automatically update to local time. The GPS I am using is a Garmin although I've had the same issue using my phone as the tracker. After returning home as I load the GPX tracklog into the map module the track is invariably offset by the time difference between my home time zone and the local time zone where the track was recorded. The photos always have the correct capture time. Therefore, I have to use the offset to match the track times with the photo times. For example, just came back from a 9 hour time zone difference trip. A photo taken and time stampted at 2:00 pm matches the track time of 5:00 am. I've not yet tried loading the GPX track while traveling to see what happens. Can anyone offer an explanation as to what is happening.

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1 reply

johnrellis
johnrellis
Legend
October 31, 2018

The necessity for telling LR the offset is due to the ancient EXIF spec that didn't allow time zones to be recorded for photos' capture times.

GPX tracklogs record their timestamps in UTC (GMT), whereas most cameras record whatever time you've set the camera's clock to.  (Until recently, the EXIF spec didn't even include a field for time zone.)  When LR compares the time recorded in a tracklog with the time recorded in a photo, LR converts the times in the tracklog to the time zone of the computer running LR, and it assumes the photo's capture time is also in that time zone.

If the camera's clock was set based on the same time zone as your computer, you don't need to use LR's Set Time Zone Offset command. For example, suppose your computer is in San Francisco and set to PST (UTC - 8), and you set your camera's clock in PST.  LR will consider a photo whose capture time is "14:00" to be 14:00 PST (22:00 UTC).  It will then look for a point in the tracklog with time close to 14:00 PST (22:00 UTC).

But suppose you travel to New York, you set your camera to the local time, EST (UTC - 5), and you took a photo at 14:00 EST (19:00 UTC).  That photo will have 14:00 recorded in it (but with no time zone).  You go home and load the tracklog and photo into LR on a computer set to PST (UTC - 8).  LR will assume that the photo was taken at 14:00 PST (22:00 UTC) rather than the actual 14:00 EST (19:00 UTC), and it will look for a point in the tracklog with time close to 14:00 PST (22:00 UTC).

That's not what you want, but there's no way for LR to know which time zone a photo was taken in.  So you need to use the Set Time Zone Offset command to specify the offset between your computer's time zone and the time zone where you took the photo (more precisely, where you set your camera's clock).

The most recent EXIF spec (2.31, July, 2016) finally included an EXIF field for cameras to record the time zone of the capture time. But most cameras in use still don't record that field, even though many allow you to pick the time zone when you set the clock, and many know the time zone automatically (e.g. smart phones and cameras with GPS units).  Some cameras record the time zone in proprietary locations.

Given Adobe's lack of attention to metadata, Library, and the Map module for the past many years, and given how clunky the catalog internal architecture is for storing capture times, I think it's unlikely they'll ever change the map module to use any time zone recorded in EXIF.  But you never know -- you could file a feature request in the official Adobe feedback forum: Lightroom Classic CC | Photoshop Family Customer Community

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