Personal Geotagging: Data wrangling

I recently learned that the process of cleaning datasets so that they can really be used is called “data wrangling”.

At first, I thought that the main data wrangling task in personal geotagging was going to be cleaning the GPS data. Sometimes the GPS is too coarse, sometimes it’s off because not enough satellites were in view, sometimes the GPS was just not turned on when I took the photo.

But, in the course of resetting my cameras’ clocks to standard time today, I realized that I’m going to have to wrangle the timestamps on the photos as well. I had thought that one-hour increments due to daylight savings and time-zone travel would be the main problem, but now I see that the minutes matter, too. Camera clocks don’t sync with the network or with GPS (at least not on my relatively ancient cameras), and I can move a significant distance in the three or seven minutes by which the clock has drifted away from GPS time.

I’m going to have to be able to apply short time offsets to the timestamps of all photos taken by a given camera on a given day. Setting the correction is going to require precisely recognizing at least one key location in each batch of photos in order to compute the offset.

That’s for past photos. For the future, I can get in the habit of either correcting the clock frequently or of snapping a reference shot with my cellphone along with each set of camera shots.

Space-time is tricky.

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