metasync

README

metasync

For years I shot with a Canon 6d, which had an integrated GPS. I've upgraded to a Canon r5 mk II, better in every way except that it has no integrated GPS. This has led to two issues:

• some photos files have the wrong time in their EXIF data
• most photo files do not have any GPS data

The r5 mk II can sync with a phone and use its GPS to populate its GPS data, so for days when I remember to sync with the phone, I will have usable GPS data.

Unfortunately, I often go several months without shooting, and without GPS data to fix the factory default clock settings, my photos end up without any coordinate data and bad timestamps.

metasync fixes this.

usage

$ metasync --target photos/without/metadata/ --target more/targets/ --ref phone-photos/from/same/period --ref more/reference/photos/

Both --target and --ref may be provided multiple times to scan more than one directory per side.

metasync is a local web-based tool that allows you to use a known good set of images as a kind of GPS tracker. If you have a photo in the ref set that is taken about the same time as a photo in the target set, you can typically use that to fix all of the photo timestamps in the target set.

From there, you can use the ref GPS coordinates to fix the target GPS coordinates using a variety of strategies.

installing

Unfortunately you will need a working Go build environment. Fortunately this is generally pretty easy to get. Either use go.dev/dl to download an official package, or brew install go, or your other package manager of choice.

From there:

$ go install github.com/jmoiron/metasync

Should download, build, and place metasync in $GOPATH/bin. You may want to add that directory to your $PATH.

How it works

When you first run metasync, it will parse all of the exif data from your files create thumbnails for them. This is typically quite fast, because most digital photos have thumbnails already in the EXIF data, and metasync will simply extract these if present.

From there, you're presented with the interface in the screenshot above.

If the timestamps on your images are wrong, the first and most important step is to fix them. Hopefully, you have two images that were obviously taken at the same place around the same time. In practice, I often do end up with this, either a backlit exposure that I wanted to use the phone for, a selfie, etc.

Selecting a target and ref photo and clicking "Add Pair" will add this set of photos as a synchronization pair. Clicking "apply" will adjust the timestamps on all of the photos in scope using the delta from that pair.

But what is a scope?

scopes

The scope dropdown defines 3 scopes: "global", "session", and "single image".

These scopes define how broadly the changes we've defined will apply. The default scope is "global", and this is probably the right scope for fixing the timestamps on a large set of photos, as typically you only need to find one good pair to compute the delta for the rest of the photoset.

The "session" scope is a heuristic grouping of photos. Photos are in the same session of each photo in the sequence has a time gap of less than the session time. The default time is session time is 5 minutes, which means if photo N and photo N+1 are taken within 5 minutes of each other, they are in the same session. This ends up being a pretty handy way to separate out strings of photos by where they were taken, because you are typically not snapping a lot of photos while in transit.

The final scope is "single image", which applies changes only to the target image that has been selected. This is useful for small fixes, like selecting a GPS location from a map for a photo that was not part of other sessions but is in a well known place.

Fixing your photos

Typically, you will want to use "global" scope to fix the timestamps and to do a first pass of GPS coordinate fixing.

There are two "auto" strategies for fixing coordinates:

• closest reference timestamp
• interpolated position between stradling images

Lets say target image T1 is taken at t=30, with ref images R1 and R2 taken at t=10 and t=40. The "closest reference timestamp" strategy will simply adopt the GPS coordinates from R2, which has a closer timestamp to T1. The interpolated strategy will attempt to perform linear interpolation between the two coordinates, using the timestamp of T1 to determine where along that line it should be placed. In practice, "closest reference timestamp" works pretty well, but the interpolation can be useful if eg. you were taking photos from a moving vehicle.

The auto-coordinate fixing has a cut-off time proximity where it won't consider a reference photo as a match for the target photo. By default, this is 30 minutes, but you may want to constrain this more for the global application if you are very concerned about accuracy.

From here, you can use the "missing gps" lens (a checkbox at the top) to see what photos still don't have GPS coordinates, and you can change the scope to session or single-image depending on how broadly you want to apply your updates.

There are three simple fixes you can apply to the smaller scopes: "from ref image", "from prev target", and "from map".

The "from ref image" button copies the GPS data in the selected ref image to all of the photos in the scope. If you have photos that you know were in the same location (eg. at the AirBnB you were staying at) but are not close in time, you can use this to fix them.

The "from prev target" can be good when you have a brief break taking photos and then resumed in the same location, but not close enough to any ref photos, eg. photos taken before and after a dinner.

Finally, "from map" allows you to use the map in the metadata section under the target photos to click on a location for that photo. If you don't have any phone photos available, but a session or a specific photo was taken from a well known location (eg. a landmark), you can use this to set it manually.

Up until this point, no changes have been made to your photos. To apply the changes to the files on disk, you can click the red "save" button.