Author Topic: Daylight Saving Time  (Read 12593 times)

Offline Kirk Baker

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Re: Daylight Saving Time
« Reply #15 on: February 22, 2013, 06:47:36 AM »
Hayo,

Cameras (really the EXIF Capture Time tag) has no provision for GMT Offset at all.  The computer's GMT Offset is always used from the host computer.  This much has always been true in Photo Mechanic (at least as long as I can remember.)

DST is enabled/disabled on the host computer.  In countries (or states/provinces) that don't observe DST, the DST offset would always be zero.  I know for certain that Mac OS X can automatically determine when to apply DST but I don't know if Windows does offhand.  PM 5 is now asking the computer: Is DST in effect now?  If it returns NO then the GMT Offset is not modified.  It shouldn't matter which day a particular country/county/state/province enables it as long as it is observed consistently on your computer system.

If this turns out to be an actual issue for you all, we'll be sure to make a preference in an update build to make it off by default and folks like Warren can turn it back on.

Hi Kirk, I'm still a bit confused. What does this fix actually change? if I look at the exif data, I do see times with e.g., +09:00 (which is correct as they were taken in Japan) or +01:00 (which is my own time zone). I guess, with daylight savings in effect at the time the shot was taken the times should actually read +10:00 and +2:00? Is this what your fix does?

As a side note: I found my newer cameras do actually record both the DST flag as well as the timezone (as e.g.,+ 09:00), older camera's only register the timezone, or nothing of this sort at all.
I think, ideally, PM should be able to adjust these fields in the Adjust Capture Times in the tool menu. This way you can correct mistakes properly (forgotten to set DST, or change the timezone).

We may entirely undo the change.  I have sent Warren a private message about this issue along with the research I have done on it.  Most cameras don't put any information about the UTC offset or whether DST was in effect at the time of capture.  Some of the newer Nikon models do put this information into their MakerNotes.  It is not information that PM can rely upon and it isn't always realistic to use the computer's UTC/DST offset for the photos anyway.

As for PM adjusting the MakerNote data, I haven't discussed this with the rest of the team.

-Kirk

Online Hayo Baan

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Re: Daylight Saving Time
« Reply #16 on: February 22, 2013, 10:12:03 AM »
Hayo,

We may entirely undo the change.  I have sent Warren a private message about this issue along with the research I have done on it.  Most cameras don't put any information about the UTC offset or whether DST was in effect at the time of capture.  Some of the newer Nikon models do put this information into their MakerNotes.  It is not information that PM can rely upon and it isn't always realistic to use the computer's UTC/DST offset for the photos anyway.

As for PM adjusting the MakerNote data, I haven't discussed this with the rest of the team.

-Kirk

Right, perhaps this is the best thing.

And I indeed shoot mostly Nikon and they do seem to include more meta data than the Canons I've shot with so far (not their latest models though so things may have improved there too). Updating the timezone etc. maker notes from within PM would be awesome of course, but not top prio as I can always use exiftool if I want to.
Hayo Baan - Photography
Web: www.hayobaan.nl

Offline jwvaughn

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Re: Daylight Saving Time
« Reply #17 on: February 22, 2013, 12:16:00 PM »
DST is enabled/disabled on the host computer.  In countries (or states/provinces) that don't observe DST, the DST offset would always be zero.  I know for certain that Mac OS X can automatically determine when to apply DST but I don't know if Windows does offhand.  PM 5 is now asking the computer: Is DST in effect now?  If it returns NO then the GMT Offset is not modified.  It shouldn't matter which day a particular country/county/state/province enables it as long as it is observed consistently on your computer system.
-Kirk

Kirk,

I suspect that Windows (long time user) and Macs work pretty much the same way in that within a specific time zone with DST enabled, they both can determine if the DST offset is needed.  However there is a large caveat. Without precise location data, there is no way of knowing if DST is being observed by a subset locale of the time zone.

I have to admit to a hazy recollection on this but it is either Utah observes DST and some tribal areas do not or Arizona does not observe DST but some tribal areas do or perhaps both. (I spent two weeks in the area border area of Arizona and Utah was never sure what the local time was!)

I have not looked at Windows time zone choices extensively but I wonder if they have all the time zones in the world covered?  I was acquainted with a guy who wrote a book about the time zones of the world and when all the local anomalies are accounted for, there are somewhere over 100 different zones.

Sorry to pontificate about this but the time zone problem is considerably more complex than most folks realize. If time is really that important to a photographer, I would suggest setting the cameras to GMT and geotagging the photos from which local time can be derived.

Jerry

P.S. Just for fun http://en.wikipedia.org/wiki/IANA_time_zone_database
« Last Edit: February 23, 2013, 12:47:51 AM by jwvaughn »

Offline Andreas Yankopolus

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Re: Daylight Saving Time
« Reply #18 on: March 02, 2013, 01:10:55 PM »
A simple way to do this would be to put "camera time zone" and "local time zone" dialogue boxes on the import menu. When traveling, it's handy to keep your camera(s) and GPS logger set to UTC, then deal with time zone changes on import.