Geotagging - What's It All About?

Add GPS information to your digital photographs

Posted: 10 July 2009
by Dave Mycroft

Most of us have taken pictures when out walking, and months or years later while flicking through we can't remember where on Earth a picture was taken. By combining data from a GPS with data from a digital camera it’s possible to record the exact time and location of any digital photograph. The combined file tells you everything you could want to know about the photograph, from the camera it was taken with to the exact longitude and latitude or Grid Reference.

How it works
When a digital camera records a picture, it saves a data file to the camera's memory. The data that makes up the image makes up the majority of the file, but along with the image itself the camera also records information about how the image was taken. If you right click on an image on your PC and select Properties you'll see everything from the type of camera used, and its aperture and speed, to the picture's dimensions.

If you’ve set the clock on the camera or phone camera you’ll know exactly when the picture was taken, but that's probably not going to help much in remembering exactly where it was taken after a few months. The data file that holds all the technical information on your picture, called the EXIF (Exchangeable Image File Format) file, also has a few more fields that are empty by default including fields for longitude and latitude. By combining the digital data generated by a GPS and the photograph's EXIF file you can make a permanent record of the exact location the shot was taken from.

Since geotagging became popular around 2007 a number of digital cameras have hit the market with dedicated GPS interfaces, and software to automate the procedure and share the results has become widespread. By the middle of last year the popular photo sharing site, Flickr, had 2.3 million geotagged images, and today geotagging photgraphs onto Google Earth is becoming commonplace.

Geotagged images can be shared online at sites like Flickr

Once the photographs are geotagged, they can be used in lots of different ways. The most obvious use is to catalogue photographs by location, or associate them with a particular walk like the West Highland Way. With digital mapping of millions of walkers' computers you can mark interactive links on maps to show the view. Google Earth and Google Maps can have geotagged photographs linked directly to their locations, and you can follow a trail or trek in photographs before setting off.

Geotagging your pictures
There's three ways to combine the GPS data into a picture's EXIF file; manually from a tracking file, using software that accepts both file types or using a camera with a direct GPS connection. Almost every digital camera on the market, including most mobile phone cameras, produces EXIF files and can export the data or save it to a flash memory card. If you already know the exactly where the picture was taken applications like Microsoft Pro Photo Tools allow you to manually drag a file onto a map to place and tag it, saving the information direct5ly to the EXIF file.

For automated entry programs like the free Photomapper software can take both images and GPX data from a PC or memory card and combine the two sets data into the EXIF file. GPS manufacturers have also started producing receivers with preloaded software to reference your photographs with data from the tracklog, making it possible to geo-tag any image which has a time stamp.

The next step up is to completely automate the process and have the photos geotagged before they even leave the memory card. Devices like the ATP Photofinder Mini combine the functions of a GPS receiver with an SD card slot to accept your camera's memory card. Simply make sure your GPS and Camera clocks are set at the same time, turn the Photofinder on and off you go - at the end of the day put your camera's SD card in the slot and the location data will be automatically transferred to the EXIF file.

The ultimate solution, of course is to integrate a GPS into the camera but, at least for now, this isn't available at high street prices. Cameras like Nikon's D300 have an interface for connecting a GPS directly to the camera, but at the price the improved accuracy is negligable over automated or semi-automated software providing the clocks on GPS and camera are synchronised fairly closely. For the majority of walkers a couple of seconds isn't going to make much difference to your location.

Some high end cameras have a direct connection GPS interface

Verdict
Geotagging is just getting out of its infancy and becoming popular. With the increase in freely available digital mapping and satellite imagery, and the widespread use of GPS, it's got potential. Being able to remember where you took your photos is certainly easier if they're geotagged, but it's when you publish or share the images that it really comes into its own. It's one thing seeing your route plotted on a map, but to have points along the route tagged with photographs means you can use them for much more accurate descriptions. Highlights and dangers can be identified, and you can share the information on Google Earth or Google Maps. For the average hill walker geotagging may seem a bit more hassle, and maybe more time or expense, than it's worth - but take a look on your computer and see just how fast we accumulate pictures with today's camera and you'll soon see the advantages.

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