I purchased a dashcam a while ago because (1) people drive like absolute idiots where I live (seriously, watch that video) and (2) who knows what you might capture? It’s a Viofo A129 Pro Duo, it has a 4k front-facing camera and an additional HD rear-facing camera. It also has built-in GPS.

Because it’s always on, I figure it would be nice to use the footage for mapping purposes as well! The process is not completely straightforward, hence this blog post.

Let’s look at what the camera produces:

Just movie files, no separate GPX files. That means the location information must be embedded in the video stream somehow. Great..

Some internet sleuthing reveals that the fantastic image / video metadata swiss army knife exiftool (tagline: Metadata R Us 🤣) picked up support for extracting location metadata from video files a few years ago! The command to use is

exiftool -p gpx.fmt -ee -ext mp4 -w %f.gpx ~/tmp/*.MP4

You can read the exiftool documentation to learn more about the various parameters. What’s important is that you need the gpx.fmt file that is basically the template that exitfool uses to write out the raw location data to the familiar GPX format. You can grab it from here.

In the above form, exiftool will iterate over an entire directory of .MP4 files and write one GPX file for each. For this demo, I just copied one movie file from the SD card, so the result is one GPX file with the same name as the movie file but with the .gpx extension.

Now that we have the companion GPX file, we can use mapillary_tools to extract individual images, add location information and upload everything in one step:

mapillary_tools video_process_and_upload 
    ~/tmp/ 
    --skip_process_errors 
    --geotag_source gpx 
    --geotag_source_path ~/tmp/20221209_130755_00330F.gpx

Because the Mapillary CLI tools can only take a single GPX file as the location metadata input, a little scripting to process an entire folder of images would be really nice. I will follow up in another blog with more on that.

I am also experimenting with the camera’s time lapse mode. The video feed for the front camera alone is more than 2GB per 5 minutes, meaning on longer trips you run out of storage and the camera overwrites older files. I will post more on this in the near future as well.

My conclusion is that this definitely could be easier, but it’s also very doable if you’re not afraid of the command line.

Finally, some links for reference:

• The original dashcam video
• The Mapillary sequence is still processing as I write this, but you’ll be able to find it on my Mapillary user page once it’s done.
• Mapillary Tools on Github
• exiftool