Multiplex: Small multiple artwork from GPX tracks

I’d seen the small multiple artwork of running and cycling routes from Marcus Volz’s R package Strava all over the web. Ads for “posters of your GPS tracks” pop up on Reddit and I’d notice a few #Rstats people put up their posters on Twitter. I’ve had the package bookmarked for a while and this week I finally got round to generating a small multiple poster of some of my cycling routes.

I was pleased with the result and wanted to post it here. But also, running the code was not straightforward as I’ll explain below. If you want to generate your own plot read on.

The idea behind the poster is really nice. You get a kind of generative art-style poster. It looks nice and you can identify individual routes which is fun to do.

The instructions on the GitHub page are absolutely correct and the code should run out-of-the-box. The idea is that you download your Strava data and then make your plots. Unfortunately, it seems that a change in Strava’s data export policy (possibly related to GDPR changes) has broken the package. I found that there are two problems. First, Strava’s “download your data” link gives you a mix of formats (in my case GPX and FIT files), the package only works with GPX. Second, if there is any elevation data missing from a track, the data frame that is needed to make the poster is not built properly.

Going GPX only: In my case, I don’t keep all my data in Strava and instead use a local repository managed with RubiTrack. This software allows me to filter for the tracks I want and export them in GPX format. The only problem is that it generates one huge file with all the tracks enclosed. This gets read by the package as a single track. To fix this, I split the file using awk.

awk '/<trk>/{close(file);n++;}{file="track"n".gpx";print >> file;}' untitled.gpx

I could then discard track1.gpx which just had the xml header and then use the directory of gpx files.

The elevation problem: this affected only some of the tracks, so in the end the R code needed to be modified. The elevation data is not needed to make the posters so the file process_data.R needs editing, line 28 can be commented out and then line 32 should read:

result <- data.frame(lat = lat, lon = lon, time = time, type = type) %<%

This issue is raised on GitHub and has been closed, but the code doesn’t work with elevation blanks. If you run into this problem, this is the way I found to fix it. The other plots in the package which do use elevation will not run, but at least the poster can be made.

I exported the poster as PDF and then made some changes in Illustrator to give the result above.

The post title comes from Multiplex from Oliver’s Standing Stone LP from 1974.

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