Hands on: Location, location, location

Adding GPS position data to your photos could be much easier than you think

We're going to take a Hands On look at geotagging. This is the process of adding positional data, usually but not necessarily obtained from a sat-nav device, to digital images. I’ve been experimenting to try to find the best way to do the job.

I’d been manually adding latitude and longitude data to photos using Google Maps by going to http://maps.google.co.uk, zooming in on the required location and copying the data from the ‘link to this page' link.

For a few photos this approach is workable, as long as you’re familiar with the area in question. But it’s labourious and time-consuming. Even if you don’t have a GPS receiver, an increasing number of photo-editing applications provide the means to add geopositional metadata to your photos.

Google Picasa lets you Geotag your photos using Google Earth. Selecting ‘Geotag with Google Earth’ from Picasa’s Tools > Geotag menu launches Google Earth and a Picasa window with your image thumbnails appears in the lower-right corner of the screen. Then you simply select the shot, find the location using Google Earth’s navigation controls and press the Geotag button.

Using maps to geolocate photos makes things easier, but it’s still time consuming and error-prone. It’s usually straightforward to geolocate photos shot in an urban environment where you have plenty of buildings and landmarks to help you out. But finding rural locations can be a different matter. One field can look much like the next, and what if you want to geotag photos that were taken on a cruise or in flight?

Go with GPS
The only answer to this problem is to carry a GPS receiver with you and use software on your PC to match up your photos with location data from the GPS track log.

Digital camera and photo accessory manufacturers are becoming aware of the interest in geotagging and it is only a matter of time before more sat-nav device manufacturers follow suit. If you’re looking for a dedicated geotagging sat-nav, there is a handful of units from which to choose, including Sony’s GPS-CS1. Though designed for the CyberShot range, it can be used with any camera. There’s also the Gi STEQ Photo Tracker and Jobo’s Photo GPS, which fits into your camera’s hot shoe.

The devices work in the same way. Time-referenced positional data is recorded in a track log file, which is downloaded to the PC and cross-referenced with images via the Exif time information recorded when they were taken.

If you have no other use for a sat-nav device, then these are small, inexpensive and doubtless do a good job. But if you already own a GPS receiver, or are thinking of getting one for in-car use, hiking, cycling or other outdoor pursuits, then you can also put it to geotagging use.

On track
I’ve been using a couple of handheld devices to record a GPS track log with which to geotag photos and I’ve had mixed results.

Both devices functioned well and did everything they claimed to in terms of functionality, but while the Garmin Etrex Vista Cx proved well suited to the task of Geotagging, Magellan’s Explorist 500 was more problematic.

In large part, this was due to the fact that the Robo Geo software I’ve been using to acquire the tracklog data and apply it to images is designed to work directly with Garmin units. Having said that, the fact that Magellan’s USB driver wouldn’t install and I had to copy the tracklog from the device memory to an SD card, then use a card reader to import it, didn’t help. This didn’t get me very far as the Explorist tracklogs are stored in a text file that Robo Geo doesn’t recognise.

If you already own a Magellan device you can probably convert the text files to a standard format that Robo Geo can read. A good tool for converting tracklog files between the multitude of available formats, including mapping formats such as Microsoft’s Autoroute, is GPSBabel.

In practice, there’s very little you need to do other than set up the GPS device and – this is crucial – synchronise your camera’s clock with that of the sat-nav unit. The GPS system gets its time from the orbiting satellites, so you can assume it’s accurate. It’s essential that the two clocks are synchronised because Robo Geo gets the date and time information from a photo’s Exif data, then looks up the positional data with the corresponding time in the GPS tracklog. If you forget to synchronise the two devices, Robo Geo and some of the applications mentioned later allow you to specify a time offset.

To ensure synchronicity you must set your GPS receiver to record tracklog data by time rather than distance, and to set a relatively short time interval. If you don’t, it’s possible for the track log to record data at locations before and after you arrived at your location, but not at the actual spot where you took the photo. You’ll need to work out the best interval to ensure that adequate points are recorded without prematurely filling the sat-nav’s memory or, if the device has one, SD card.

Then all you have to do is make sure the unit is switched on and pop it in your camera bag.

Using Robo Geo
On returning from your photoshoot, download your images in the usual way and launch Robo Geo. See the Further info box for details of where to download it and for details of the other geotagging applications mentioned here. The personal licence version of Robo Geo costs $39.95 (about £20). You can download a free trial, but this introduces a deliberate error of up to 1km in the positional data, so it’s of little practical use.

You can select individual images or an entire folder; Robo Geo supports TIFF, PNG, BMP, JPG and DNG. You can’t automatically Geotag PNG and BMP files, because they don’t contain Exif time stamp data, but you can add this information manually to the Robo Geo database. If you’re wondering what use this might be, you could always resave the files as JPEGs or write the geopositional data to the image file as a caption strip along the bottom.

Connecting the Garmin Etrex Vista Cx to the PC and pressing the F3 key automatically downloads the tracklog and populates the Latitude, Longitude and Altitude data fields alongside each image. If your hardware and software combination doesn’t support direct connection you’ll first need to save the tracklog on the GPS receiver, usually in GPX format, before transferring it to the PC and importing it into your tagging application. Though less convenient than a direct connection, this way you at least have a permanent copy of the track log which, unless saved, will be overwritten when the GPS receiver’s memory becomes full.

All that now remains is to decide how you want to attach the location data to the photos. The most obvious choice is to add it to the GPS Exif metadata, so that it’s permanently stored in the image file for you to make use of at any time in the future. You can also have it automatically stamped in caption format along the bottom of each photo.

Robo Geo has some other useful automated geotagging functions. Export to Google Maps automatically creates a Google Map web page for a folder of photos, complete with thumbnail information windows linked to photo pages. You must sign up for the Google Maps API and get a key to use this feature.

There’s also an export for Flickr option, which uploads your photos to Flickr, creates new sets as required and adds the geotagged, geo:lat and geo:lon tags.

These features are useful timesavers and once the positional metadata has been added to your images it can be used in any application that supports it. You can set up your Flickr account to automatically import GPS metadata from your photos, tag them and place them on the Flickr Yahoo map.

Other software
Robo Geo isn’t the only way to automatically add latitude and longitude co-ordinates from a GPS tracklog to your photos. Microsoft’s WWMX Location Stamper matches up data from a GPS tracklog saved in GPX format and adds it to the Exif header in JPEGs. It also provides a simple way to add geopositional data if you don’t have a GPS receiver – you just drag and drop your photos onto a map.

Gpic Sync is an open-source application with lots of useful geotagging features. It works with GPX and NMEA tracklog files and supports JPEG and some RAW file formats. Like Robo Geo, it supports elevation data if present, and will automatically create Google Earth KML and KMZ files and Google Maps pages.

Further info
Magellan
Garmin
Sony’s GPS-CS1
Gi STEQ Phototracker
Jobo photoGPS
Robo Geo
WWMX Location Stamper
Gpic Sync
GPSBabel
Google Maps
Google Maps API