Introduction

Over the last few years geocoding images has become just as normal as processing images using special software like Adobe Photoshop Lightroom. There are several ways of geocoding an image, each technique with his own advantages and disadvantages.

In this tutorial I would like to focus on my solution using a smartphone with build-in GPS and special software to record a log of coordinates. Together with your images the log file can be used to geocode them by adding the coordinates. Special software will add geographic information to your images by comparing the timestamps from the log with the timestamp of an image.

Step 1: using your smartphone as a GPS logger

The first step is to log your locations to a file at a regular interval. Several solutions for this exists, like dedicated GPS loggers. I decided to use my Windows Mobile based smartphone with a built-in GPS, since I carry it around all the time. A search on the internet lead me to the free program GPSTracka, a GPS logging application for Windows Mobile. The following description is found on the homepage "This application uses the GPS receiver on your Windows Mobile phone to log your coordinates to a log file at regular intervals. Its purpose is to track your movements while you are out so that when you get back home, you can import those files and use it with whatever application accepts GPX or KML files". There are many more programs available, each with different features. You can use other programs as long as it is able to store the GPS information in a file on regular intervals.

After installing GPSTracka I have set it up with a polling rate of 60 seconds and to store to file on my memory using distinct points in the GPX format (through the options). After logging my trip I place the corresponding GPX file from my phone with the photos. Once this is done it is time to move to the second step.

Step 2: synchronize the GPS log with the images

The second step involves synchronizing the datapoints in the GPX file with the images and store the information in the EXIF of each image. The easiest way to do this is by comparing timestamps.

NOTE: EXIF stands for Exchangeable image file format and is a format to store metadata in image files.

But what if an image was taken a few seconds after an entry in the GPX file? Matching those by hand would be quite difficult and updating the EXIF information manually can become a drag real soon.

Luckily the internet provides us with another solution: the freeware program GeoSetter. One of the features of this wonderful program is the synchronization of images with track files. The GPX format we get from GPSTracka is one of the many supported formats

Another wonderful feature is the fact it can adjust the time so the time from the GPX file matches the time from the camera. In case you failed to synchronize the clocks on both devices you can still match a location to an image.

NOTE: you might want to synchronize your camera clock with the clock on the phone prior to logging.

It also allows you to interpolate regarding shoot time and allow for a maximum time difference between taken dates and trackpoints. You might want to experiment with the number of seconds used in that particular option. It all depends on how many points where recorded, which in turn depends on the availability of the GPS signal. I have found that the GPS on my phone doesn't perform well inside a building. After leaving the building it also takes a while to get a good fix again. Setting a large value for this option will allow the program to synchronize images taken inside a building with the either the last point before entering the building or the first point after leaving it.

You might notice not all images being geocoded, depending on the available data. This can be fixed by using this program, because it can also geocode manually by providing the coordinates or pointing to a location on the map. Upon saving the coordinates all information is entered in the EXIF of the photo.

NOTE: to use this feature your computer must have an active internet connection

NOTE: Using the excellent GPS Support Plugin for Adobe Photoshop Lightroom by Jeffrey Friedl you can geoencode your images from inside Adobe Photoshop Lightroom).

Congratulations! Your images are now geocoded

After storing the coordinates in the EXIF the information is also available in a range of other software packages like Adobe Photoshop Lightroom or Google Picasa. Websites like Flickr also support the available coordinates inside the EXIF. (Note Geosetter also supports writing the coordinates to an XMP sidecar file commonly used by Adobe Photoshop Lightroom (among others) to store meta information. XMP stands for Extensible Metadata Platform and is a standard format for processing and storing standardized and proprietary information relating to the contents of a file.)