Many times I have already made the attempt to utilize geo-tagging – the use of a GPS geo location device to “tag” or mark the location a photo had been taken. I have been a regular and enthusiastic user of Garmin GPS devices since the year 2000, when I bought my first $99 Garmin eTrex – the little yellow box that faithfully helped me to find the hiking track on some mountain meadow or my car’s parking spot in a large unknown city.
The basic idea for geo-tagging is actually simple: If you carry a (powered on) GPS device with you while you are taking photos, and that device has any kind of track logging mechanism, you can combine the information from the GPS tracker with the photo, use a location lookup service in the Internet to find out the street address for the longitude / latitude position the GPS recorded (now that sounds awfully simple, doesn’t it?), and tag your photos (read: add keywords) with the address information for easy searchability in your image archive.
The logical connection between a photo and the GPS track can either be made by the time stamp each photo and GPS track has – given that you somehow sync the clocks of the GPS and the camera – or by a cable connection between the GPS and the camera which allows the camera itself to write the position information into the photo right when it arrives on your memory card.
As I had always only planned to do some geo-tagging, I had carried the GPS tracking device with me while taking pictures, and dutifully saved the track path data on my hard disk. I had not really prepared the data for geo-tagging, nor had I connected the GPS device and the camera itself. So I had implicitly chosen the first approach: I have photos on my hard drive with the EXIF information when the photo had been taken, and I got GPX files for my location information for many days in the past 8 years – not all of them will have accompanying photos…
The challenge to clean this mess up will be documented in a series of posts where I will outline the software I use, and the solutions I find.
So to get back into geo-tagging and GPS-device-using mood I had recorded a track last Saturday on a bike tour that was really meant to explore the bike route from my home to the Ismaninger Speichersee birding area. I did not take my camera with me this time, but let’s see how far can we get in terms of visualizing the trip.
For read out of the track data from the GPS device to the desktop computer, I am since many years using the freeware program EasyGPS from Topografix. This nice tool has the advantage of fully supporting the GPX file format for GPS data, which is XML-based and can be read and written by many different GPS-related software packages, as we will see.
So when I fire up EasyGPS:
- The only thing I do is to click on “Receive”, select the Tracks checkbox in the dialog box and click on OK. With the Garmin Venture HC I am now using and which sports a USB interface, the resulting download takes only a few seconds.
- The resulting track data is stored on disk calling File… Save… from the menu, and selecting a directory where all my GPX GPS data files reside. I use an ISO timestamp time prefix in the form 20090506-explanationOfTrack.gpx filename to allow easy sorting of the directory.
The one challenge is that the EasyGPS will always download all data from the GPS device, so if you had not cleared out the device’s memory before recording a new track, you will end up with replicate data in the new file with the last one you downloaded. We will clean that up with the second software package:
For doing anything interesting with the track data (remember, no photos yet!) I use the also freely available tool GPS-Track-Analyse.NET from gps-freeware.de. Sorry, no international translations available as far as I can see, it seems to have a German website only. But Dietmar Domin, who has developed the tool and is maintaining this web page might be able to help you as he had requests and downloads from all over the world already!
So what I do in GPS-Track-Analyse after I opened the GPX file I just saved with EasyGPS:
- Scan the list of tracks in the middle window to determine if there is old data from previous sessions in the file (because I forgot to clean the GPS device’s memory before starting the new trip), and whether the device somehow has broken up my trip into multiple pieces (which can happen when the device was turned off, or has lost satellite reception for too long).
- The stale track data I just delete by clicking on the list item with the right mouse button, and select Track löschen to get rid of it.
- The fragmented tracks can be reconnected by using the right-click menu item Verbinden, and selecting all fragments to be put into one track. I usually rely on the time information to determine if a track needs to be merged or not (I seldom have more than one track per day that should not be connected).
- After this cleanup, I do revisit the smoothness of the height data recorded and might choose to smoothen this a little bit with the Trackpoints bearbeiten… Höhenprofil glätten… menu item. This is especially important for the tracks recorded with my old Garmin eTrex – the new chipset of the Garmin Venture HC (the “H” in the product name indicates it has this new chipset) is delivering much better data for this application in every respect. If you don’t have one of the H models yet, go out and get it now! You won’t believe the improvement in terms of accuracy and speed over the old models until you see it.
- Save your work into a new GPX file. Remember, Al says <start of quote> save early, safe often. <end of quote>
The exciting part starts only now: Use the Export function to create a file with your track for Google Earth. I do select the KMZ Archive, use the speed for the color of the track and turn off the trackpoints. The application will open Google Earth with your track in all it’s beauty, and from there you can save it to a KML or KMZ file that you can share with others.
As an example, here is a map of my my 30 km bike tour from last Saturday, where we were touching (but not circling) the Ramsar area Ismaninger Speichersee.
The color shows my speed with green being slowest and red being fastest. I will spare you the legend and min/max values 
To be continued…
Oh – positive suprise! The aggregated disk space curve actually flattens roughly mid-2009, despite my fears of faster image data growth after I had upgraded the camera to more Megapixels and Megabyte per image. What is the explanation? Well, it’s actually two:
Photoblogs.com