When we were in Spain, we took our i-Blue 747 GPS track logger with us and left it running most of the time when we were out with the cameras. I was expecting that it would be a simple matter to geocode the photos when we returned.
But it turned out that there were a couple of snags to overcome first.
Firstly, although the logger is quite sensitive and will pick up a signal indoors in many cases, it does not like being carried in my fanny pack – the material was too thick or the orientation of the logger was wrong, and we didn’t get any tracks logged most of the time. Which was a disappointment. Fortunately I had carried it in my hand or put it down on the car roof on a number of occasions while we were photographing, so I did have some tracks to play with.
In order to geocode (digital) photographs, you need to have to set the camera’s date and time, so that later a program can match the time stamp in the EXIF data in your photos with GPS track recorded by the GPS logger. When you get back to your computer, here are a few things that I have learnt:
Use a Photo-editor which preserves the EXIF data
The EXIF (Exchangeable Image File Format) data is embedded in your photograph and contains information such as the camera model, shutter speed and aperture used and among other things, the date and time at which the picture was taken.
If you edit the photos – for example, cropping or adjusting the exposure – I found that Adobe Photoshop Elements does not write the EXIF data to the new image file. Which means that the time stamp gets discarded. Apple’s Preview program (if you only want to resize pictures, for example), and The Gimp (which you can download as a Mac install package from Sourceforge) do not have this problem, so before you indulge in an orgy of editing your pictures, make a test and check whether the time stamp survives in your favourite graphic editor!
Program to edit EXIF data on the Mac
If you have destroyed your EXIF data, as I did using Photoshop Express on some of the photos, before I realised what was happening, you can add it manually (I had the original pictures in another directory, but didn’t want to have to re-edit them, so I knew the time stamp values), Reveal is an excellent free program which you can use to insert the most important data into the photo again.
Program to add the location data to your photos
The actual goal is to geotag your photographs, and after some experimenting I have decided to use GPSPhotolinker which can update JPG, TIFF and many RAW formatted photographs and which was easy to use and didn’t damage any of the photos that I processed.
It can read the data extracted from your logger in GPX or TCX format. As I mentioned in an earlier post, I use Mountain Rose’s Mac TravelRecorder to download my tracks from the logger to Mac.
Uploading to an on-line photo album
I uploaded my results to Google’s Picasa online album (here the map showing where the geocoded photos were taken), but there are a number of other on-line albums which will also take your photos and show where you took them on a map. For a few tips on using these services, see this page on Early Innovation’s web site.
