I wanted to geotag all my vacation photos with
exiftool as follows:
exiftool -geotag "*.gpx" \ -geosync "19:25:42Z@IMG_7882.jpg" \ -geosync "09:16:34Z@IMG_9798.jpg" \ -ext .jpg .
where IMG_7802.jpg is a photo of my computer clock displaying 20:25:42 MEZ on 01 March 2018 (=19:25:42 Zulu), and similarly IMG_9798.jpg is a photo of my computer clock displaying 11:16:34 MESZ on 31 March 2018 (=09:16:34 Zulu). I used two such (bracketing) reference images in order to account for drift (and, indeed, the camera clock seems to have gained 26 seconds during that month).
The adjustment went fine for the reference images:
$ exiftool -datetimeoriginal -gpsdatetime IMG_7882.jpg Date/Time Original : 2018:03:01 20:25:42 GPS Date/Time : 2018:03:01 19:25:42Z $ exiftool -datetimeoriginal -gpsdatetime IMG_9798.jpg Date/Time Original : 2018:03:31 10:17:00 GPS Date/Time : 2018:03:31 09:16:34Z
But for intermediate images, the computed GPS time is significantly off, e.g. by about half an hour in the following example (a GPS time of approximately 14:32Z is what I'd expect)
$ exiftool -datetimeoriginal -gpsdatetime IMG_8888.jpg Date/Time Original : 2018:03:17 15:32:22 GPS Date/Time : 2018:03:17 15:04:13.45312997Z
Accordingly, the computed longitudes and latitudes are quite far off as well.
My educated guess is that the problem is related to the daylight saving time that started in Germany between the two reference images. Apparently,
exiftool interpretes DateTimeOriginal in local time (so first MEZ =
+0100 and later MESZ =
+0200) whereas the camera clock just keeps on ticking (approximately with a
+0100 offset throughout).
Q: How can I tell
exiftool to not assume that the camera clock (DateTimeOriginal) follows any daylight saving time rules?