Re: Time Zone.

[Bill Moseley <moseley hank org>]

On Wed, Apr 30, 2008 at 01:52:45PM -0400, Pat Suwalski wrote:
> Tim Retout wrote:
> Disagreed. There is no such thing as a "floating date".

If a time is stored in the database w/o a timezone then you don't know
what timezone it is.  It's "floating".  Perl's DateTime objects use
this term as well for objects that do not have a timezone associated.

But, f-spot stores an epoch (as an integer) for timestamps.  That, of
course, is a point in time.

The trick on importing it making sure that the epoch you determine
from the photo is correct.

So, if the EXIF date/time does not include a timezone you need to
specify the timezone on import.  That can be used to correctly
determine the epoch for saving with the photo.

All that's needed is the timezone that the camera is using.  For the
vast majority of people that will be their local time.  Even when
traveling I suspect most do not change their camera's time zone.
But, it should be something that can be specified at import time.


Now, displaying dates of the images is a different issue.  For that
you want to store a timezone along with the image.

It will be up to the user to decide what timezone to use.  Do you want
to see all times local to the computer (which might show some photos in
daylight when the time taken shows night), or set the timezone on the
photo to reflect the location it was taken?  In that case, the photos
would display in order but the times (ignoring the timezone) might
look out of order (if photos were taken at the same moment but in
vastly different timezones).

If you happen to change the time on the camera when traveling then the
import is not going to be pretty and will need a way to adjust the
epoch stored in the database.

> 
> This is not rocket science, a user will do this if they want to. Adding 
> timezones complicates this.

That's no excuse for ignoring timezones.  Defaulting to the local
timezone for both import and display is probably smart, and makes it
simple for the user.

The act of converting from EXIF date to an epoch for the database
requires knowledge of a timezone.  So, the question is does f-spot
provide a way to select the timezone or just not provide this feature
and possibly incorrectly assume the local time zone?

And since many people to travel out of their timezone, it may not be
unreasonable to expect them to want to see the photos with the time
the event happened at the location the photo was taken, not the
time it was back at their computer running f-spot.




-- 
Bill Moseley
moseley hank org