Time zone metadata handling appears incorrect

[HarmonicDisturbance]

I am located in US Eastern timezone (GMT-04:00 when EDT). I recently noticed some pictures that were taken in France are ordered and displayed incorrectly.

I have an older camera that does not have GPS. When I travel, I leave the camera time in Eastern time. After I return I add GPS information based on pictures taken with my smartphone to these photos, and also add time offset to these photos.

A typical photo would have the following metadata:

[Composite]     GPS Position                    : <Somewhere in France>
[EXIF]          Date/Time Original              : 2016:07:05 07:34:34
[EXIF]          Create Date                     : 2016:07:05 07:34:34
[EXIF]          Modify Date                     : 2016:07:05 07:34:34
[EXIF]          Offset Time                     : -04:00
[EXIF]          Offset Time Original            : -04:00
[EXIF]          Offset Time Digitized           : -04:00

Note:

1. There are no GPS time fields
2. I have ignored the file-specific time fields
3. I have omitted the separated GPS lat / long fields as they are duplicates

However, when showing the photos in Calendar view, the display shows (for the file above) "Wed, Jul 05, 2016, 7:34 AM GMT+2", the GMT+2 reflecting the French time zone.

Furthermore, the photo appears to sort incorrectly. There is another photo taken from a phone with the following time data:

[EXIF]          Date/Time Original              : 2016:07:05 13:32:45
[EXIF]          Create Date                     : 2016:07:05 13:32:45
[EXIF]          Modify Date                     : 2016:07:05 13:32:45
[EXIF]          Offset Time                     : +02:00
[EXIF]          Offset Time Original            : +02:00
[EXIF]          Offset Time Digitized           : +02:00

This photo has no GPS data but it displays as "Wed, Jul 06, 2016, 1:32 PM GMT+2". Based on converted time, the first photo should appear after this photo but it appears before.

My understanding is that in the absence of GPS time data, the photo create time should be normalized based on the date fields and time offset, not GPS time zone. Thus both photos should be normalized to UTC which is:

• 11:34:34H for photo 1
• 11:32:45H for photo 2

Then sorted accordingly, but Photoprism appears to ignore or mishandle the Offset Time fields.

[HarmonicDisturbance]

Upon further digging I'm going to answer my own question. Found this page: https://docs.photoprism.app/developer-guide/metadata/exif/#notable-behaviors.

So GPS location overrides time offset. EXIF does not have a prescriptive method for tie-breaking, and PhotoPrism appears to follow the Apple / Google convention.

Oh well.