geotag.photos
What is a GPX Track Log?
GPX (GPS Exchange Format) is an open XML standard for storing GPS data. A GPX track log is a timestamped record of your journey — a sequence of track points, each containing your exact position at a specific moment in time.
Every track point in a GPX file looks like this:
<trkpt lat="48.8566" lon="2.3522"> <ele>35.4</ele> <!-- elevation in meters --> <time>2025-06-15T14:23:07Z</time> <!-- UTC timestamp --> </trkpt>
HoudahGeo reads these track points and matches each photo's capture timestamp to the appropriate position on the track. For complete details on GPX and other GPS file formats, see GPS File Formats Guide.
Getting a GPX File
You need a GPX track recorded during your photo shoot. Here are the most common sources:
- GPS device + manufacturer software: Export from Garmin Connect, Suunto app, Polar Flow, etc. Most support GPX export natively.
- GPSBabel: Free open-source tool that converts 100+ GPS formats to GPX. Essential if your device uses a proprietary format. Available at gpsbabel.org.
- iPhone GPS tracker apps: Apps like Trails, GPX Tracker, and OsmAnd export GPX directly. Keep your phone in your pocket — no dedicated device needed.
- Android GPS tracker apps: The same category exists on Android — look for apps that export GPX or NMEA.
- Sports watches: Garmin, Polar, Suunto all export via their companion apps. Your fitness data becomes your photo location data.
HoudahGeo Supports Multiple Formats Natively
HoudahGeo reads GPX, NMEA, Garmin FIT, and Wintec TES files directly — no conversion needed for these formats.
Step 1 — Load Photos and GPS Track
Load Your Photos
Drag and drop photos from Finder into the HoudahGeo window, or use Load > Add Photos from Files…. HoudahGeo reads the capture timestamp from each photo's EXIF DateTimeOriginal field.
Photos appear in the list showing filename, capture time, and current location status (assigned, unassigned, or GPS data from camera).
Load the GPX File
Drag your .gpx file onto the HoudahGeo window, or use Load > Import Track Logs and Waypoints from Files…. The track appears on the built-in map. You can load multiple GPX files for multi-day trips — HoudahGeo handles them all together.
Step 2 — Process: Geocode and Verify
How Timestamp Matching Works
When you run Process > Geocode using GPS data…, HoudahGeo performs interpolation for each photo:
- Find the track point recorded immediately before the photo's capture time
- Find the track point recorded immediately after the photo's capture time
- Calculate the photo's position along the route between those two points, proportional to elapsed time
The result is a precise location estimate — even if the GPS wasn't logging at that exact second. A 10-second logging interval is sufficient for most photography.
Camera Clock Adjustment — Critical for Accuracy
GPS track matching is only as accurate as the clock synchronization between your camera and the GPS device. Even a small offset means photos are assigned to the wrong location.
One Minute Off = Over a Kilometer Wrong
A camera clock off by just one minute means locations off by over a kilometer if you were traveling at 60 km/h. Always set your camera clock before a trip, and use HoudahGeo's clock correction tools when needed.
HoudahGeo offers three methods to configure the camera clock offset:
Photo Time Method
Photograph a reliable time source — your phone's clock screen or a GPS display. HoudahGeo calculates the exact offset between camera clock and GPS time from that reference photo.
Manual Method
Enter the camera's time zone and clock drift in seconds directly. Use this when you know the exact offset from a prior calibration.
Photo Location Method
Tell HoudahGeo where a specific photo was taken by pinning it on the map. HoudahGeo reverse-calculates the time offset from the GPS track.
Reviewing on the Map
After geocoding, all photos appear as pins on the built-in map. Click any photo in the list to see its assigned position. Zoom to satellite view to verify locations against recognizable landmarks.
If a photo landed in the wrong spot — perhaps because you stopped moving and the GPS drifted — drag its pin to the correct location.
Step 3 — Output: Write EXIF/XMP to Files
Writing GPS Metadata to Your Photos
Choose Output > EXIF/XMP Export… to permanently embed metadata into your photo and video files.
Which files get updated: Choose to write only to geotagged photos, or limit the export to your current selection.
Which fields get written: You control exactly what metadata is embedded:
- Timestamp and time zone
- Location coordinates (latitude & longitude)
- Altitude, heading, viewing direction, speed, water depth
- IPTC location names: city, province/state, and country (added during the Process step via reverse geocoding)
- Title / headline, description / caption, keywords
- Creator and copyright information
XMP sidecar handling: Three options let you control how HoudahGeo interacts with .xmp sidecar files:
- Write to sidecar if present — uses an existing sidecar; writes directly to the image or video file if none exists
- Always use sidecar — creates a sidecar if missing, never touches the image or video file
- Write to photo file, ignore sidecar — always writes directly to the file
Create Copies: Write to copies of your files, leaving originals untouched.
Notify Apple Photos: Once the export completes, HoudahGeo can update the Apple Photos library for any photos it manages — so the location appears correctly in the Photos app too.
The Complete Workflow at a Glance
- Before your shoot: sync your camera clock, start your GPS tracker
- Shoot normally — GPS records your track in the background
- After the shoot: load photos + GPX file into HoudahGeo
- Apply clock offset correction if needed (Photo Time Method)
- Review locations on the map; drag any incorrect pins
- Export EXIF/XMP to write GPS data permanently to files