Geotagging involves tagging each photograph with the exact location at which it was taken. Once tagged the photos can then easily be display on a map which is really useful if you are trying to remember where they were taken (you already know the when from the timestamp). I've tried manually tagging some of my photos in the past but it is a very slow and painstaking process. Of course if you have a GPS device then you can know precisely where you are and all you have to do is make use of the information to tag the photos. While many people may have GPS in their cars this isn't a lot of good if you are walking around. To solve this problem what you really need is a very small GPS recorder.
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I did have a few problems getting it to work initially. As I said it doesn't seem to ever get a location fix inside (which is where I was when I was first trying it out) and on the day I bought it I managed to crash it. Basically there are two versions of the software on the supplied CD (v3 and v4) which both have slightly different capabilities. As it turns out some of the advanced features found in v3 aren't compatible with the hardware and this combined with the software locking up on my laptop left the device rather confused and I had to wait 12 hours for the battery to go flat before I could re-charge it and get it to respond.
I also, as yet, haven't managed to give it a really good test on a long day out, but I did record my journey to work this morning from Penistone train station right to the department at the university and took some photos on the way. The results of this can be seen on the Google Maps below (or if you prefer you can view it in Google Earth).
One of the main let-downs of the bundled software is that while it will output both KML and KMZ files for viewing in Google Maps and Google Earth respectively only the KMZ output links to the photos and the format the software produces doesn't work properly with Google Maps. Anyway a bit of hacking later gave me a KMZ file that works OKish in both -- expect me to write software that does this better at a later date.