How to Geotag Photos After the Fact Using GPS Track Logs
Not every camera writes GPS coordinates into photos automatically. Most professional DSLRs, mirrorless cameras, and older compact cameras have no built-in GPS receiver. If you use one of these cameras for field photography, your images will have accurate timestamps but no location data — unless you use a process called track log geotagging to add coordinates after the shoot.
Track log geotagging works by matching the timestamp recorded in each photo against a GPS track log recorded at the same time on a separate device. At each timestamp, the track log provides the corresponding GPS coordinates — and those coordinates are written into the photo's EXIF data. The result is a fully geotagged set of images from a camera that had no GPS capability of its own.
What is a GPS track log?
A GPS track log is a time-stamped sequence of location records — latitude, longitude, altitude, and timestamp — recorded at regular intervals by a GPS device. The most common format is GPX (GPS Exchange Format), an open XML standard supported by virtually all GPS devices, sports watches, cycling computers, and mapping apps. Other formats include KML tracks (produced by Google Earth and some Google apps) and FIT files (produced by Garmin sport devices).
The density of the track log — how frequently a new coordinate is recorded — determines how accurately coordinates can be interpolated to match a photo timestamp. A track log with one recording per second provides very precise position data for fast-moving scenarios. A track log with one recording per minute is adequate for walking-pace field surveys where position changes slowly.
How track log geotagging matches timestamps to coordinates
The geotagging software reads the DateTimeOriginal field from each photo's EXIF data, then searches the GPX track log for a matching time. If the exact timestamp is present in the track log, that coordinate is used directly. More often, the photo timestamp falls between two track log entries — in that case, the software interpolates a position between the two nearest entries in proportion to the time difference.
For example: if a photo was taken at 10:15:30, and the track log has entries at 10:15:20 and 10:15:40, the software calculates a position that is halfway between those two coordinates (since the photo is equidistant in time from both entries). This interpolated coordinate is then written into the photo's GPS EXIF fields.
This approach is accurate to within the GPS device's positioning precision — typically 3 to 10 metres for consumer devices — as long as the camera clock is correctly synchronised to the GPS device's time. Clock synchronisation is the most important prerequisite for accurate results.
Clock synchronisation — the critical requirement
If the camera clock is offset from the GPS device clock by even a few minutes, every photo will be geotagged with a position from the wrong time — potentially placing photos hundreds of metres or more from where they were actually taken, depending on the speed of movement.
Before any field session that will use track log geotagging, synchronise the camera clock to a GPS-verified time source. The simplest method is to take a photo of your smartphone screen showing the exact GPS time, then compare that to your camera's DateTimeOriginal value after the shoot to calculate any offset. Most geotagging software allows you to apply a time correction offset to shift all timestamps by a fixed amount before matching.
Recording a GPS track log in the field
Several options are available for recording a GPX track log during a shoot:
- Smartphone apps: apps such as OsmAnd, ViewRanger, Wikiloc, and GPSLogger for Android can record continuous GPX tracks in the background while you work. GPS Logger is particularly useful — it is lightweight, records at configurable intervals, and exports GPX files directly. On iOS, apps such as Trails, Gaia GPS, and OsmAnd serve the same function.
- Dedicated GPS loggers: small battery-powered devices that clip to a camera bag or belt and record a continuous track to a memory card. Popular models include units from Columbus, GlobalSat, and Garmin. These are reliable for full-day shoots where a phone battery may not last.
- Sports and activity watches: Garmin, Suunto, and Polar watches that record tracks for running, hiking, or cycling can export GPX files via their companion software or directly from the device's file system.
- Garmin inReach: a satellite communicator that records tracks even in areas without mobile phone coverage — useful for remote field work.
Software for track log geotagging
ExifTool (command line)
ExifTool by Phil Harvey is the definitive tool for EXIF manipulation and supports GPX track log geotagging directly. The command to geotag a folder of images against a GPX file is straightforward. ExifTool interpolates coordinates, writes GPS fields into the original files (or copies), and supports time offset correction. It runs on Windows, macOS, and Linux and is the tool of choice for batch processing large shoots.
digiKam
digiKam is an open-source photo management application with a built-in GPS track log correlation tool. It provides a visual interface for matching photos to a track log, reviewing the proposed coordinates on a map before writing them, and adjusting the time offset interactively. Good choice for photographers who prefer a GUI workflow.
Adobe Lightroom with GPS track import
Adobe Lightroom Classic supports GPS track log import via the Map module. After importing a GPX file, Lightroom automatically correlates photos within the shoot time to track log coordinates and displays them on the map. Coordinates can then be written into the image metadata.
GeoSetter
GeoSetter is a free Windows application specifically designed for photo geotagging from GPS track logs. It provides a split view of the photo list and a map, with tools for manual coordinate adjustment, time zone handling, and GPX import with automatic correlation.
After geotagging from a track log, load your photos into GeoMeta Pro to verify that GPS coordinates were written correctly. Check the map view to confirm that plotted positions match the expected locations from your field visit. Any images showing missing or anomalous coordinates can be identified quickly before filing the final report.
Verifying geotagged results with GeoMeta Pro
Once your track log geotagging software has processed the photos, load the full batch into GeoMeta Pro to review the results. The GPS tagged percentage should now reflect the full set, not just the images that had native GPS data. Use the map view to visualise the photo positions and switch on the Walk Path to check that the sequence of positions follows a coherent route consistent with your actual field visit.
If any photo positions look wrong — clustered in the wrong area, placed in the wrong order along the route, or showing coordinates that are clearly inconsistent with the visit location — this is usually a sign of a clock offset that needs to be corrected and the geotagging re-run. Export the verified results as KML, GeoJSON, or CSV for your records or GIS workflow.
When to use track log geotagging
Track log geotagging is the standard approach for professional field photographers, wildlife researchers, archaeologists, geologists, landscape photographers, and any workflow where a dedicated camera is preferred over a smartphone but GPS-tagged images are required. It adds a small amount of pre-shoot preparation and post-shoot processing, but produces fully geotagged images indistinguishable from those taken on a GPS-equipped device.