I just realized that now all my files' "Date Modified" are 1 hr off after daylight savings time. This is obvious when you compare the Date Modified vs EXIF date picture taken.
After some research, I learned that the Date Modified timestamp is recorded in UTC. Then it is displayed with the current timezone adjustment. So before DST, if I had a file modified at 14:00 UTC, and my timezone was PDT(-7), then Windows file explorer would display the time stamp as 7:00, which was correct. But now that it is DST, which is PST(-8), Windows is displaying the time stamp as 6:00, which is incorrect.
Is there a way to have Windows XP display the correct time stamp? I think it should take into account the date of the timestamp and figure out whether it was during DST or not. So a timestamp of 6/1/2009 14:00 would be adjusted -7:00 to 7:00 (since 6/1/2009 was during DST). Whereas a timestamp of 1/1/2009 14:00 would be adjusted -8:00 to 6:00 (since 1/1/2009 was not DST).
On Nov 2, 9:21 am, bucky3 <buc...@mail.com> wrote:
> So before DST, if I had a file modified at 14:00 UTC, and > my timezone was PDT(-7), then Windows file explorer would display the > time stamp as 7:00, which was correct. But now that it is DST, which > is PST(-8), Windows is displaying the time stamp as 6:00, which is > incorrect.
Correction:
So *DURING* DST, if I had a file modified at 14:00 UTC, and my timezone was PDT(-7), then Windows file explorer would display the time stamp as 7:00, which was correct. But now that it is *NO LONGER* DST, which is PST(-8), Windows is displaying the time stamp as 6:00, which is incorrect.
> On Nov 2, 9:21 am, bucky3 <buc...@mail.com> wrote: >> So before DST, if I had a file modified at 14:00 UTC, and >> my timezone was PDT(-7), then Windows file explorer would display the >> time stamp as 7:00, which was correct. But now that it is DST, which >> is PST(-8), Windows is displaying the time stamp as 6:00, which is >> incorrect.
> Correction:
> So *DURING* DST, if I had a file modified at 14:00 UTC, and > my timezone was PDT(-7), then Windows file explorer would display the > time stamp as 7:00, which was correct. But now that it is *NO LONGER* > DST, which > is PST(-8), Windows is displaying the time stamp as 6:00, which is > incorrect.
Why is it incorrect? The file was modified at a fixed time, to which is either added or not an hour. 06:00 normal time => 07:00 summer time. 14:00 - 8 hours => 06:00.
If you always want "wall-clock" time displayed for files, store then on a FAT-16 file system. Possibly even a FAT-32 volume, but I haven't checked that.
> "bucky3" <buc...@mail.com> wrote in message > news:5072e4d8-79c4-4ffd-82a7-9ff4205ebbeb@u36g2000prn.googlegroups.com... >> On Nov 2, 9:21 am, bucky3 <buc...@mail.com> wrote: >>> So before DST, if I had a file modified at 14:00 UTC, and >>> my timezone was PDT(-7), then Windows file explorer would display the >>> time stamp as 7:00, which was correct. But now that it is DST, which >>> is PST(-8), Windows is displaying the time stamp as 6:00, which is >>> incorrect.
>> Correction:
>> So *DURING* DST, if I had a file modified at 14:00 UTC, and >> my timezone was PDT(-7), then Windows file explorer would display the >> time stamp as 7:00, which was correct. But now that it is *NO LONGER* >> DST, which >> is PST(-8), Windows is displaying the time stamp as 6:00, which is >> incorrect.
> Why is it incorrect? The file was modified at a fixed time, to which is > either added or not an hour. 06:00 normal time => 07:00 summer time. > 14:00 - 8 hours => 06:00.
You're both wrong :-) When going DST, you don't change timezones. You stay in the same timezone, but apply DST.
In this time zone, June 21st, 12:00 is the way to denote a specific moment in time(*), and there is only one way to denote a specific moment in that time zone. If you went to lunch at 12:00 on that day, you aren't going to tell you went to lunch at 11:00 if you tell a story about it later in winter (unless it's used as an alibi and you are trying to fool a detective).
So if a file has a June 21st 12:00 timestamp, the computer should always display it as June 21st 12:00 as long as it is set up in that time zone, whether DST applies or not. Of course, if the computer is configured in the next timezone, then the same timestamp can be displayed as June 21st, 11:00, and this will be the correct display in summer and winter in that time zone.
> So if a file has a June 21st 12:00 timestamp, the computer should always > display it as June 21st 12:00 as long as it is set up in that time zone, > whether DST applies or not. Of course, if the computer is configured in > the next timezone, then the same timestamp can be displayed as June > 21st, 11:00, and this will be the correct display in summer and winter > in that time zone. [] > Bertrand
Yes, I can see your argument, but if you take it to its logical conclusion, wouldn't you need to include the different time zone of the taking device in your calculation of displayed date as well as the time zone of the display device, so pictures taken at the same instant would show a different timestamp if they were taken in New York, London or Paris?
David J Taylor wrote: > "Ofnuts" <> wrote in message news:4aef509d$0$12528$426a74cc@news.free.fr... > [] >> So if a file has a June 21st 12:00 timestamp, the computer should >> always display it as June 21st 12:00 as long as it is set up in that >> time zone, whether DST applies or not. Of course, if the computer is >> configured in the next timezone, then the same timestamp can be >> displayed as June 21st, 11:00, and this will be the correct display in >> summer and winter in that time zone. > [] >> Bertrand
> Yes, I can see your argument, but if you take it to its logical > conclusion, wouldn't you need to include the different time zone of the > taking device in your calculation of displayed date as well as the time > zone of the display device, so pictures taken at the same instant would > show a different timestamp if they were taken in New York, London or Paris?
A timestamp is absolute. In computers it is stored as the number of seconds (or milliseconds, or nanoseconds) since a reference time (00:00 UTC on January 1st, 1970 for Unix and a lot of web-related things)(*). Whether it is later displayed as June 21st, 12:00 or June 21st, 09:00 depends only on the "reader". In other words the timezone is nothing more than a parameter when displaying or parsing date representations, and unless it is implicit (but with computers, "implicit" is seldom a good idea) it should be part of the display or input string. Giving a time as "2009/11/03 12:00" without a time zone is a bit like giving an appointment at 12:00 but not telling which day. So, ideally, your three cameras would attach the very same time stamp to the three photos.
However, the people who did the Exif standard overlooked the timezone/DST problem. The timestamp is stored as a "YYYY:MM:DD HH:MM:SS" character string, and doesn't include a time zone. So this information is lost and if the three cameras above are on local time, they will store a different timestamp string. If the standard had provided for a time zone, they would have stored something like "2009/11/03 12:00 UTC+0" in London, "2009/11/03 13:00 UTC+1" in Paris, and "2009/11/03 07:00 UTC-5" in NY which are three different representations of the very same timestamp.
And the cherry on the cake is that the FAT/FAT32 file system used in memory cards uses local time, and files are often transferred between camera and computer using a card reader, so unless the camera is carefully kept on local time things can get quite fun later, for instance when geotagging the pictures.
> A timestamp is absolute. In computers it is stored as the number of > seconds (or milliseconds, or nanoseconds) since a reference time (00:00 > UTC on January 1st, 1970 for Unix and a lot of web-related things)(*).
.. conveniently forgetting about things like leap seconds, perhaps?
> Whether it is later displayed as June 21st, 12:00 or June 21st, 09:00 > depends only on the "reader". In other words the timezone is nothing > more than a parameter when displaying or parsing date representations, > and unless it is implicit (but with computers, "implicit" is seldom a > good idea) it should be part of the display or input string.
Agreed.
> Giving a time as "2009/11/03 12:00" without a time zone is a bit like > giving an appointment at 12:00 but not telling which day. So, ideally, > your three cameras would attach the very same time stamp to the three > photos.
That would depend how the users have the cameras set, of course.
> However, the people who did the Exif standard overlooked the > timezone/DST problem. The timestamp is stored as a "YYYY:MM:DD HH:MM:SS" > character string, and doesn't include a time zone. So this information > is lost and if the three cameras above are on local time, they will > store a different timestamp string. If the standard had provided for a > time zone, they would have stored something like "2009/11/03 12:00 > UTC+0" in London, "2009/11/03 13:00 UTC+1" in Paris, and "2009/11/03 > 07:00 UTC-5" in NY which are three different representations of the very > same timestamp.
.. and once lost, it's gone forever.
> And the cherry on the cake is that the FAT/FAT32 file system used in > memory cards uses local time, and files are often transferred between > camera and computer using a card reader, so unless the camera is > carefully kept on local time things can get quite fun later, for > instance when geotagging the pictures.
> (*) see "epoch" on Wikipedia > -- > Bertrand
It can also be fun if:
- you take pictures before the time-change, and upload them to your computer afterwards.
- you take pictures in one time-zone and upload them in another
and I'm sure you can think of even more circumstances. For those reasons, I keep my camera set to UTC rather than local time, and I don't change it between summer and winter. I don't bother about leap seconds on the camera, as its clock isn't accurate enough to warrant it.
It is an important point to know that Windows displays the time with the actual date, and the current offset time, rather than the time offset for the taking date.
> "Ofnuts" <> wrote in message news:4af004ab$0$25364$426a74cc@news.free.fr... > [] >> A timestamp is absolute. In computers it is stored as the number of >> seconds (or milliseconds, or nanoseconds) since a reference time >> (00:00 UTC on January 1st, 1970 for Unix and a lot of web-related >> things)(*).
> .. conveniently forgetting about things like leap seconds, perhaps?
No, they are taken in account (assuming the display and parsing code are correct (mostly the display, since most serious computers self-synchronize via NTP).
>> Whether it is later displayed as June 21st, 12:00 or June 21st, 09:00 >> depends only on the "reader". In other words the timezone is nothing >> more than a parameter when displaying or parsing date representations, >> and unless it is implicit (but with computers, "implicit" is seldom a >> good idea) it should be part of the display or input string.
> Agreed.
>> Giving a time as "2009/11/03 12:00" without a time zone is a bit like >> giving an appointment at 12:00 but not telling which day. So, ideally, >> your three cameras would attach the very same time stamp to the three >> photos.
> That would depend how the users have the cameras set, of course.
This assumes that the cameras would have a way to know the "absolute" time (ie, set to UTC, or given a timezone).
> It is an important point to know that Windows displays the time with the > actual date, and the current offset time, rather than the time offset > for the taking date.
Not even sure of the date part. If a file is stamped at 00:30 on June 21st, will Window show it later as stamped at 23:30 on June 21st or at 23:30 on June 20th?
>> "Ofnuts" <> wrote in message >> news:4af004ab$0$25364$426a74cc@news.free.fr... >> [] >>> A timestamp is absolute. In computers it is stored as the number of >>> seconds (or milliseconds, or nanoseconds) since a reference time >>> (00:00 UTC on January 1st, 1970 for Unix and a lot of web-related >>> things)(*).
>> .. conveniently forgetting about things like leap seconds, perhaps?
> No, they are taken in account (assuming the display and parsing code are > correct (mostly the display, since most serious computers > self-synchronize via NTP).
>>> Whether it is later displayed as June 21st, 12:00 or June 21st, 09:00 >>> depends only on the "reader". In other words the timezone is nothing >>> more than a parameter when displaying or parsing date >>> representations, and unless it is implicit (but with computers, >>> "implicit" is seldom a good idea) it should be part of the display or >>> input string.
>> Agreed.
>>> Giving a time as "2009/11/03 12:00" without a time zone is a bit like >>> giving an appointment at 12:00 but not telling which day. So, >>> ideally, your three cameras would attach the very same time stamp to >>> the three photos.
>> That would depend how the users have the cameras set, of course.
> This assumes that the cameras would have a way to know the "absolute" > time (ie, set to UTC, or given a timezone).
>> It is an important point to know that Windows displays the time with >> the actual date, and the current offset time, rather than the time >> offset for the taking date.
> Not even sure of the date part. If a file is stamped at 00:30 on June > 21st, will Window show it later as stamped at 23:30 on June 21st or at > 23:30 on June 20th?
There is no easy universal way around these problems. Fortunately in the grand scheme of things it's not a big deal as long as you are aware of what's happening. If one is that picky, set the camera to UTC, keep it that way and just do a mental adjustment as needed.
Thanks everyone, that was quite an educational thread.
Just curious, how do other operating systems (like Unix, Mac) handle the file timestamp in regards to DST? Do they have the same problem, or do they handle it better?
On Tue, 3 Nov 2009 20:57:14 +0000 (UTC), Toxic <staring@my_hd.tv> wrote:
>On Tue, 03 Nov 2009 13:56:43 +0000, David J Taylor wrote:
>> I keep my camera set to UTC rather than local time
>Good idea, >and since I've got to go in and dither its clock one of these days, >I think I'll do likewise.
My camera (Nikon D300) is set to synchronise time with my computer every time I connect the two. The computer (Windows XP) shows local time, including the adjustment for DST. It also is synchronised daily with a time signal from somewhere (USN Hawaii?) All of this is very convenient and much more meaningful than me having to maintain my camera at UTC.
On 2009-11-03 13:25:30 -0800, bucky3 <buc...@mail.com> said:
> Thanks everyone, that was quite an educational thread.
> Just curious, how do other operating systems (like Unix, Mac) handle > the file timestamp in regards to DST? Do they have the same problem, > or do they handle it better?
Apple provides an option for automatic date & time setting via one of 3 online time servers; Apple Americas/U.S. (time.apple.com); Apple Asia (time.asia.apple.com); Apple Europe (time.euro.apple.com) this automatically handles all DST issues.
In article <2009110313342154666-savageduck1@REMOVESPAMmecom>,
Savageduck <savageduck1@{REMOVESPAM}me.com> wrote: > > Just curious, how do other operating systems (like Unix, Mac) handle > > the file timestamp in regards to DST? Do they have the same problem, > > or do they handle it better?
> Apple provides an option for automatic date & time setting via one of 3 > online time servers; Apple Americas/U.S. (time.apple.com); Apple Asia > (time.asia.apple.com); Apple Europe (time.euro.apple.com) this > automatically handles all DST issues.
other time servers can be added and the time stamp is utc with a time zone offset.
>> Thanks everyone, that was quite an educational thread.
>> Just curious, how do other operating systems (like Unix, Mac) handle >> the file timestamp in regards to DST? Do they have the same problem, >> or do they handle it better?
>Apple provides an option for automatic date & time setting via one of 3 >online time servers; Apple Americas/U.S. (time.apple.com); Apple Asia >(time.asia.apple.com); Apple Europe (time.euro.apple.com) this >automatically handles all DST issues.
So does Microsoft. And other organizations. But the time transmitted is always UTC and any time zone settings are handled locally on your computer according to your timezone settings. After all, how would the server know if you are on the left side or right side of that time zone border.
bucky3 wrote: > Thanks everyone, that was quite an educational thread.
> Just curious, how do other operating systems (like Unix, Mac) handle > the file timestamp in regards to DST? Do they have the same problem, > or do they handle it better?
I believe the Unix-based systems (Linux, OSX, BSD) handle it correctly.
Eric Stevens wrote: > On Tue, 3 Nov 2009 20:57:14 +0000 (UTC), Toxic <staring@my_hd.tv> > wrote:
>> On Tue, 03 Nov 2009 13:56:43 +0000, David J Taylor wrote:
>>> I keep my camera set to UTC rather than local time
>> Good idea, >> and since I've got to go in and dither its clock one of these days, >> I think I'll do likewise.
> My camera (Nikon D300) is set to synchronise time with my computer > every time I connect the two. The computer (Windows XP) shows local > time, including the adjustment for DST. It also is synchronised daily > with a time signal from somewhere (USN Hawaii?) All of this is very > convenient and much more meaningful than me having to maintain my > camera at UTC.
It's also a lot easier if you geotag your photos using a GPS log file.
bucky3 <buc...@mail.com> wrote: >Just curious, how do other operating systems (like Unix, Mac) handle >the file timestamp in regards to DST?
It's not an issue because all times/dates are stored in UTC (or actually seconds since the epoch) and converted to local time for display purposes only.
>Do they have the same problem, >or do they handle it better?
Not sure how you define "problem" and "better". The exact time is available, it is up to you as a user to decide how you want to display it.
I think your problem is not a problem at all. Or maybe it's a problem where there is no meaningful solution. Or maybe you didn't think it through all the way. DST is only one very small factor in dealing with local time.
Example: If photos have been taken in Sydney at lunch time and now you are looking at those files back home in NewYork, what time stamp would you expect: 13:00 (the local time at the place those files were created) or 22:00 the previous day (the local time of when the files were created at the place you are looking at the files now)? Now imagine that you uploaded those files minutes after you took them to your home server in NY, and another family member uploaded some other photos locally in NY 2 hours later. What time sequence would you like to see: your photos first or his photos first? Because by local time based on where the photos were taken his would be first by 13 hours although they were taken 2 hours after yours.
So no, there is no golden bullet and the only sensible option is indeed using UTC and thus having an absolut target, that is not moving with crossing each time zone boundary and not moving with every switch between DST and non-DST, either.
> My camera (Nikon D300) is set to synchronise time with my computer > every time I connect the two. The computer (Windows XP) shows local > time, including the adjustment for DST. It also is synchronised daily > with a time signal from somewhere (USN Hawaii?) All of this is very > convenient and much more meaningful than me having to maintain my > camera at UTC.
> Eric Stevens
If you want better than a daily sync, look at NTP:
>> "Ofnuts" <> wrote in message >> news:4af004ab$0$25364$426a74cc@news.free.fr... >> [] >>> A timestamp is absolute. In computers it is stored as the number of >>> seconds (or milliseconds, or nanoseconds) since a reference time >>> (00:00 UTC on January 1st, 1970 for Unix and a lot of web-related >>> things)(*).
>> .. conveniently forgetting about things like leap seconds, perhaps?
> No, they are taken in account (assuming the display and parsing code are > correct (mostly the display, since most serious computers > self-synchronize via NTP).
Unix time ignores leap seconds, at least according to:
and that's my experience as well. The "number of seconds" does /not/ include the leap seconds. To test, try seeing whether the Unix time tor the start of a day is exactly divisible by 86400 - e.g. 1257292800 (4-Nov-2009 at 00:00:00). If Unix time included the leap-second count, the start of a day should be n * 86400 + 24. (IIRC).
[]
> Not even sure of the date part. If a file is stamped at 00:30 on June > 21st, will Window show it later as stamped at 23:30 on June 21st or at > 23:30 on June 20th?
> -- > Bertrand
An interesting point, although to some extent one I face all the time as, for example, most of my "daytime" photographs taken in Australia cover two UTC calendar days. As my camera and hence my EXIF information stays on UTC, the photos have a continually increasing sequence number when renamed, even over a winter/summer time change. My photos have a name - typically:
David J Taylor wrote: > "Eric Stevens" <> wrote in message > news:5s71f5p6ertaenre4l8uk09cetnbhhbc50@4ax.com... > [] >> My camera (Nikon D300) is set to synchronise time with my computer >> every time I connect the two. The computer (Windows XP) shows local >> time, including the adjustment for DST. It also is synchronised daily >> with a time signal from somewhere (USN Hawaii?) All of this is very >> convenient and much more meaningful than me having to maintain my >> camera at UTC.
>> Eric Stevens
> If you want better than a daily sync, look at NTP:
> You can keep your PC within a fraction of a second using an Internet > connection.
You don't need "NTP for Windows" with Windows you know. The Windows Time Service is quite capable of synchronizing to an NTP server, and in fact Vista does that out of the box unless it's on a domain, in which case it synchronizes to the domain controller.
On XP and earlier you have to do some digging to set it up, on Vista it's set up right off the clock application in the system tray on the lower right. For XP the procedure can be found at http://support.microsoft.com/kb/314054#EXTERNAL. There's a link from there to the procedure for Windows 2000.
> You don't need "NTP for Windows" with Windows you know. The Windows > Time > Service is quite capable of synchronizing to an NTP server, and in fact > Vista does that out of the box unless it's on a domain, in which case it > synchronizes to the domain controller.
> On XP and earlier you have to do some digging to set it up, on Vista > it's > set up right off the clock application in the system tray on the lower > right. For XP the procedure can be found at > http://support.microsoft.com/kb/314054#EXTERNAL. There's a link from > there > to the procedure for Windows 2000.
Yes, the Windows Time Service will provide a basic synchronisation, but not to within a fraction of a second. With XP, the default sync interval was one week, IIRC, by which time a poor PC clock could be tens of seconds out. There are a number of reasons to prefer NTP over the basic Windows software, should you wish:
On Tue, 3 Nov 2009 20:57:14 +0000 (UTC), Toxic <staring@my_hd.tv> wrote:
>On Tue, 03 Nov 2009 13:56:43 +0000, David J Taylor wrote:
>> I keep my camera set to UTC rather than local time
>Good idea, >and since I've got to go in and dither its clock one of these days, >I think I'll do likewise.
For me, I only use the time stamp to sort the order photos were taken, and the particular local time doesn't matter, so I just leave my camera set on Eastern Standard Time, which is my home time zone. I could just as easily use UTC I suppose.
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