Temporal geotagging
We look at the timestamp in the metadata of the image file and compare it to the time data in the GPX track file. The best match gives us the most probable location of where the photo was taken and allows us to tag it and display it on the map.
For this to work, the image file needs to have this metadata (such as the typical EXIF tag that most digital camera’s attach to the image file) intact and not stripped. Most image manipulation software won’t strip it, though some may do so.
It also requires some degree of synchronization between your GPS device and your camera; if the clock of your camera and GPS unit are way off from each other, you’ll get significant errors (pictures won’t be shown on the right spot on the map). Typical situations where this can be a problem is with daylight savings time (GPS unit probably automatically adjusts its clock, whereas for the camera you may need to do this by hand – something you may forget to do), or while on location in a different time zone.
To resolve this problem, we’ve added the ‘Time calibration’ option. This is a tool that allows you to manually adjust the potential time conflict between the camera and the GPS unit. You simply need to enter the time you read on your GPS and the time you read on your camera, at a given instance. A simple trick to do this would be to take a photo of the display of your GPS unit (showing the time) at the end of your trip – that way you have both timestamps directly available.
