Parallelized Photo Tagging with Google Location Data

May 4, 2024

Overview

For tagging large numbers of photos, ExifTool does not include multi-core support out of the box. The workaround, recommended by its creator Phil Harvey, is to run multiple instances of ExifTool in parallel. It's not the most elegant solution, but if we run these instances automatically in the background, we can achieve rudimentary multi-core support for ExifTool.

An example script is provided below. ExifTool's GPS data tagging operation is used, because it's slow and benefits greatly from parallelization.

Script: Parallelized GPS Tagging (Linux & MacOS)

This simple script uses a log of GPS locations to recursively tag all photos in a given directory with GPS data.

Photos are correlated with smartphone location data based on the time they were taken. They're then tagged with the corresponding GPS location logged by the smartphone. This allows photos taken on an older DSLR camera to be displayed on a photo map. Multiple instances of ExifTool are launched at once to tag thousands of photos in parallel. Each ExifTool instance tags photos inside a child directory, recursively. Tagging photos with GPS metadata is achieved using a GPS track log (e.g. location tracking exported from Google Takeout) and the ExifTool geotagging feature.

#!/bin/bash

gps_log="/path-to-gps-log/Records.json"

# Find all directories in the current directory
# Excluding root directory and sub-directories
find . -maxdepth 1 -mindepth 1 -type d -print0 |

    # Loop across all directories with support for special characters
    while IFS= read -r -d '' i; do

        # Run ExifTool GPS tagging command in the background
        nohup exiftool -if 'not $GPSLongitude' -if '$OffsetTime' -iptc:all="" '-geotime<${DateTimeOriginal}${OffsetTime}' -geotag "${gps_log}" -api GeoMaxIntSecs=0 -api GeoMaxExtSecs=10800 -api LargeFileSupport=1 -overwrite_original -m -r -ext ARW -ext CR2 -ext JPG -ext JPEG -ext TIF ${i} &
    done

Here's a breakdown of the lengthy ExifTool command used above:

  • Excludes photos with existing GPSLongitude metadata: -if 'not $GPSLongitude'
  • Ensures UTC timezone offset metadata is included in the photo: -if '$OffsetTime'
  • GPS timestamps will reference DateTimeOriginal metadata combined with the UTC timezone offset: '-geotime<${DateTimeOriginal}${OffsetTime}'
  • GPS coordinates found within a 3-hour range of when the photo was taken are applied: -api GeoMaxExtSecs=10800
  • GPS coordinates are not interpolated using the closest two (no guesses): -api GeoMaxIntSecs=0
  • A GPS log file location is specified: -geotag "Location History/Records_2018.json"
  • Large file support is enabled for files >4GB
  • IPTC metadata is destroyed, because it can interfere with tagging
  • Original files are overwritten
  • Minor errors are ignored
  • Command runs recursively into all subdirectories
  • File extensions targeted are ARW, CR2, JPG, JPEG, and TIF
  • nohup ... & is applied to run the each process in the background

License: CC BY-SA 4.0 Deed - You may copy, adapt, and use this work for any purpose, even commercial, but only if derivative works are distributed under the same license.

Category: Notes, Software