I’d go for a used Garmin GPSMAP 60CSx, it can track a whole day with regular batteries and saves in GPX format.
You can get maps for free from Openstreetmap, moreover they are robust and weather resistant.
Gpslogger for Android. minimal app, with subsequent minimal impact on battery life. I’ve tracked a day long motorbike trip with v.little battery usage. Can export final track to gpx or kml. No realtime track display.
I use the same. Important is not to forget to take a picture of the phone with a clock that also shows seconds, so that you are able to correctly fill in the time when you geotag the photos.
How you do take the information from OSMand, and apply it to an individual photo? With a GPS unit attached to your camera, I believe you can see the coordinates for each photo when using say DT or RT when editing no?
There are apps and programs that can correlate the time a picture is taken with the time stamps present in a gpx track file, and write the corresponding coordinates into the picture. Hence the importance of having your phone/gps logger and camera synchronized.
While searching what “GPS Time” is, I found this interesting information. So actually, if the time given by a GPS is the “GPS Time”, it is 18 seconds ahead of the GMT. It should be taken into account if your application of timing is precise at level of the seconds.
Nothing says that the track recorder logs the GPS time. It could log the phone time. Easy to test by pressing the app’s “start” button at a know time UTC time, and then checking the time in the first GPX record.
I don’t think you need to be pedantic about this.
You have:
GPS Position Error, depending on the signal and device can be a few meters or a lot of meters
GPS Time Error (you already found that)
Camera Time Error (not all seconds are the same )
Some other error I probably forgot about
From my (limited) experience, is more than enough to match camera time with the GPS device time to get a reasonably accurate GPS tag. Disclaimer: I did not tried this from a speed train (but I did from a not speeding car) …
I geotag my photos with GPS4CAM.
During travel the app that is minimal) keeps the gps position on my iphone.
On my PC, an other app automatically synchronise and geotags photos in batch mode.
I also geotag the raws and I never had problem (but I have backups in case of problem). Once verified I keep only the geotagged files
A gpx file is generated.
I synchronise mutiple cameras with it.
In OSMand, if you go to Settings > General Settings > Global Settings > Misc, you can adjust where all the files are stored. Set something like nextcloud or syncthing to upload them.