RogerBW's Blog

I don't like being spied on. But I don't mind gathering my own data. In July of 2012 I bought a USB GPS receiver (a GlobalSat BU-353, the cheapest available device that had a good score on the gpsd compatibility list) for use with a Raspberry Pi, and I have it running for most car trips I make. (Images follow.)

The Pi is plugged into a cigar-lighter power adaptor (my car has an extra socket in the boot, which is handy for this) and a very simple piece of software records the raw output of gpsd to a file on the Pi's SSD: it's a series of lines of JSON. That can later be interpreted and overlaid onto maps; here I'm using OpenStreetMap Mapnik tiles.

So here's the map of the domestic car journeys for which I have logs.

And here's the foreign version.

Which is an interesting start. But there's much more that's possible. Every data point has a time and speed attached.

Here's a really simple example to get started with. Consider those two routes round Denmark in the foreign map above: they diverge around Hamburg in the south, and a few miles outside Copenhagen in the north. The land route (north through Denmark and a sharp right turn) took 4:25:46; the ferry route took 4:52:46. (Both of these include breaks, of course.) As far as mileage goes, the land route is about 283 driving miles, while the ferry route is about 199.

So I can now make an informed decision: is it worth saving 84 miles of driving (fuel, car wear, etc.) to pay 80-plus pounds for the ferry and take half an hour longer? Well, no.

Even though the Danish Ministry of Transport would like one to use the ferry route (I've been asked in a lay-by why we were using the road rather than the nice ferry), from this data point it seems better not to.