Fonger I use a Qstarz Btq1000
. It comes with the software you need. It is about the size of a pager.
All you do is charge it up, then turn it on when you want to log your route. If you are at a spot you want to remember, just push the button on the front of the unit. When you download the track the saved way-points will show on your map with push pins.
I have merged this files with my photos, then you know exactly where the photo was taken (within about 10 meters).
The Data logger's time is set from the gps satellite in the sky. If you do not have the time set correctly on your camera, it will not work. Remember ship's time usually is not port time. Also on some excursions, like one in Skagway you cross into Canada, and change time zones. If you do not change the time on your camera, the photos will be messed up.
Below is a map of Glacier Bay. I can match the photos with the map, and know for use what glacier I was taking a picture of.