What is it?

Digital cameras are cool. So is GPS. And, EXIF tags are really cool too.

What happens when you merge the three? You end up with a set of photos taken with a digital camera that are “stamped” with the location at which they were taken.

The EXIF standard defines a number of tags that are for use with GPS.

The program takes GPS data in GPX format. This is an XML format. I recommend using GPSBabel – it can convert from lots of formats to GPX, as well as download from several brands of popular GPS receivers.

1) The program can “interpolate” between points (linearly) to get better results. (That is, for GPS logs that are not one sample per second)

2) The resolution is down to one second. But that should be good enough for most things. (This is a limit of the EXIF tags format, as well as GPX)

3) For best results, you should synchronise your camera to the GPS time before you start taking photos. Note: digital cameras clocks drift quickly – even over a short period of time (say, a week).

Installing is easy if you are running debian unstable (sid) or Ubuntu you can just run the following command install it.

$ apt-get install gpscorrelate gpscorrelate-gui

So, here we will see if the photo’s end up on the map, and if they do, make sure they are in the correct position.

Well, that didn’t work at all.  The image on the map isn’t anywhere near where I took it!

I have several .gpx files from commuting to work and other small trips around town. What if I want to merge several files into one big file? Use gpsbabel!

What is GPSBabel?
GPSBabel converts waypoints, tracks, and routes between popular GPS receivers and mapping programs. By flattening the Tower of Babel that the authors of various programs for manipulating GPS data have imposed upon us, it returns to us the ability to freely move our own waypoint data between the programs and hardware we choose to use. It also has powerful manipulation tools for such data. It contains extensive data manipulation abilities making it a convenient for server-side processing or as the backend for other tools.

Oh, it’s also open source (free) and runs on almost every OS. Sounds perfect for a Linux user. Here is how I installed and used it on my Debian server.

Grab the source code tarball from the ‘net and compile.

$ tar zxvf gpsbabel-x.x.x.tar.gz
$ ./configure
$ make
$ sudo make install

Then my first time using the program with the merge option….

$ gpsbabel -t -i gpx -f 20120706.gpx -i gpx -f 20120707.gpx -x track,merge,title="COMBINED LOG" -o gpx -F bigtracks.gpx
GPX: This build excluded GPX support because expat was not installed.

Oh no, an error! Probably missing a library. I will need to find out what is causing the problem, fix it and recompile the program.  Some quick Googling and…..

$ sudo apt-get install expat libexpat-dev

That worked! The results of all the random .gpx files I had at the time are merged on the map below.