One of the features I enjoy with taking pictures and importing them on to my Mac, is that afterwards the Photo app can show a map of everywhere I have taken a picture. But that only works if the longitude and latitude are included in the picture. With my iPhone, that works great. With my nice (but not too nice) camera, that does not happen. However, since I am a runner, I have a GPS unit that is often keeping track of where I am. With a bit of software and know-how, I can combine the information.
The important thing is to try and get a time synchronization picture. That is a picture of the display of the GPS unit showing it running. Preferably try and get the picture while the time is showing a round number, but with the tools on this page it isn't as important. With this image you can know the difference between the time of the GPS versus the date/time on the camera. I like to keep my time as accurate as possible on the camera, but this will make it absolutely precise.
The tool, ExifTool, used in this documentation makes the assumption that you can see the UTC time on your device. Since I use a runner's GPS unit, it does not tell me that information and I need to use the operations I document here to extract it.
If you can’t get a synchronization picture, then you have to hope your camera has the exact same time as the GPS satellites. You don’t have to get the time synchronization picture at the same time as you are taking the pictures: You can start a new run of the GPS unit and take a picture then and use that to find the offset.
If you are using the Photos.app on a Mac, I have found that doing this operation on both files will destroy the link between a matched JPEG and RAW file. Before this, Photos would just recognize them as the same picture and would treat both files as one picture. After this operation, they are loaded as two separate pictures. In this case, I would recommend just deleting the JPEG, as the RAW one has more information.
You will need ExifTool to do most of the work. You can download it here. It has a page on Geotagging with ExifTool, but it doesn't give much help with the calculations that are needed. I believe it was written under the impression that the geotagging would be done in the same time zone that the pictures were taken.
If you have a heightened attention to detail, it may bother you if your pictures have a wrong time embedded within them. The exiftool can help you with this. To change the time you can use the helpful
-AllDates feature to shift each pictures time by the appropriate amount. At the same time, you can explicitly set the time zone with the
-timezone option. For completeness, you should probably use the
"-filemodifydate<datetimeoriginal" option to keep the file time set appropriately.
For example, if you crossed from a -6:00 time zone to a -7:00 time zone (you travelled west), and forgot to set the time and zone on your camera, you would need to run the following commands on the pictures:
exiftool -AllDates-=1 -timezone=-7:00 "-filemodifydate<datetimeoriginal" .
/gpx/trk/trkseg/trkpt[first()]/time: We will refer to this as the
/gpx/trk/trkseg/trkpt[last()]/time: We will refer to this as the
GpxEndTime. It is not actually necessary, but it is convenient for keeping track of which pictures you have that were taken while the GPS unit was running.
exiftool -h <<time synchronization picture file>>on it.
/table//tr[td='Date/Time Original']/td: We will refer to this as the
/table//tr[td='Time Zone']/td: We will refer to this as
TimeZoneOffset = (LocalTimeZone - CameraTimeZone) * 60 * 60
GpsTime = GpxStartTime + GpxStartTime
SyncCameraTime, taking into account the time zone difference. (The
GpsTimeis in UTC, the
SyncCameraTimeis in the camera's time zone.)
Offset = GpsTime - SyncCameraTime + CameraTimeZone
TimeZoneOffsetadded in. The ExifTool gets confused between the time zone the tool is operating in, and the time zone the picture was taken in. So you need to add the differences in time zones in.
TotalOffset = Offset + TimeZoneOffset
exiftool -geotag <<logfile.gpx>> -geosync=<<TotalOffset>> .
exiftool '-DateTimeOriginal>FileModifyDate' .
jhead -ft *.JPGto fix these files, but jhead only works on JPEG files.
You can input the values you have collected into this form and it will calculate the exact command you will need to run.
Run these commands in a folder that contains all of the pictures between and
2016-7-13: Inital writing
2016-7-29: After taking a vacation in a different time zone, and taking lots of pictures, I discovered errors with the algorithm.