Handling time information

Knowing when something happened in time is difficult when information is scares. I will try to document different scenarios and how they should be handled. The goal is always to get a timestamp in UTC time and know how to display it in local time where the image was taken.

Picture with GPS timestamp

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A picture taken with a camera that has tagged it with a GPS timestamp already has the correct information. This is the ideal situation but unfortunately not yet the most common.

Missing information

• If GPS position is missing timezone needs to be set manually

Questions

• Is it possible to have a picture with GPS time but without GPS position, GPS chips get the time before it can get a fixed position but the camera might not use it unless a complete fix is found.

Picture taken with phone

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The phone adjusts it time after both daylight savings and time zone. This might not be a 100% but close enough.

Missing information

• Timezone
• Daylight savings offset can be calculated by the date and timezone

Questions

• Can it be assumed that daylight savings should always be compensated for, there are places which does not use it?

Picture taken with digital camera with static time

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A camera that never change it's time can be synchronized to a fixed UTC offset.

Missing information

• Offset against UTC offset
• Does the camera automatically change time for daylight savings
• Timezone to know how to display it as local time

Questions

• Can it be possible to find out if camera automatically adjust for daylight savings if there are UTC offsets defined for summer period and winter period?

Picture taken with a digital with time changed on trip

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The time of the camera might be adjusted manually to always reflect local time.

Missing information

• Timezone
• Daylight savings offset can be calculated by the date and timezone

Picture taken and scanned with no exif information

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Older pictures might not have any valid exif information at all since they are scanned or similar. The problem here is that only partial information might be available such as the year.

Missing information

• Timestamp or partial time with resolution notice
• Timezone

Presentation

Date and time should always be presented in local time where the picture was taken. Thus displaying timezone information should not be needed.

If a correct timestamp exists with timezone

Monday, April 25th 2011, 08:02:40

If correct timestamp exist but no timezone

Monday, April 25th 2011, 08:02:40 UTC

If partial time information exists

2011

April 2011

Monday, April 25th 2011

Monday, April 25th 2011 08:XX:XX

Monday, April 25th 2011 08:02:XX

Monday, April 25th 2011 08:02:40