In order to save battery, many GPS-enabled cameras power their GPS receiver only once you turn on the camera. It then takes anyhwere from a couple of seconds to several minutes for the GPS to know where you currently are.
If you take a photo during this power-up phase, the camera is left with the option to use a previously recorded GPS location or forgo geotagging the photos.
At the end of the day, you will have a set of photos where some images lack geotags. This can easily be fixed with HoudahGeo.
The most straightforward way to geocode photos is to copy-paste coordinates from nearby images. Select an image that has coordinates. Then, select Copy Coordinates from the Images menu. Now, select images taken at the same location and select Paste Coordinates from the Images menu.
You can repeat the procedure for all images lacking geotags. This may however become laborious. Use HoudahGeo’s Geocode from Reference Photos feature to automate the process. This copies coordinates from geotagged reference photos to other photos taken at about the same time.
Since the photos lacking geotags may not have been taken at the exact same spot as the photos you took minutes later, you may need to adjust the coordinates that you copied over. Use the built-in map to make these adjustments.
Likewise you can use the map to copy coordinates from one image to the next. Start with a photo for which the location is known and follow the incremental geocoding workflow to fill in gaps.