![]() ![]() In order to correctly find the position of the image we need to know if it’s noon in London (UTM), New York, Berlin, Sydney or any other place of the world. ![]() All we know is that the GPX file uses UTM time (at least with my Garmin) or contains the time zone used if it doesn’t. So what exactly does a time stamp of “12:00:00” mean? Well, it’s noon, but where? Most people set it to their local time, but what is that? The image doesn’t tell us. At least on all cameras I have seen so far. The time stored in the EXIF data doesn’t contain a time zone. So we might need to fix the time stored with the image. Anyway, if the time of camera and GPS tracker differs the location will also be wrong. Maybe you are better in taking care of setting the embedded clock. At least my camera is almost always off a little. In reality there are a few problems which you need to keep in mind.įirst, most cameras don’t have the exact time (GPS devices however have it, they are basically showing the time from atomic clocks sent by the GPS system). So all we have to do is take the time stamp of the image, look-up the position of the GPS tracker at that point in time and assume that camera and GPS device were in close proximity. As you probably know, the EXIF data of the images also contains a time stamp. Basically it is a mapping between time and position, telling us where the device has been at a given time. ![]() The GPS receiver calculates its current position based on the information it receives from some satellites and stores them in a GPX file, together with the current date and time (and some other data which we are not interested in). First of all let me explain what these GPX files are. So, let me explain the intended workflow to assign geo locations to your images making use of the GPX file stored by your GPS tracker. Or just keep reading, it might be interesting after all. If you want to tag the images manually you can skip the next two paragraphs, too. If you are lucky enough to have a camera which already stores coordinates in the EXIF data of the images you can skip this paragraph and also the next one. If you just want to try this you can take the manual route but if you plan to geotag thousand of pictures taken during your vacation I would advice to spend a little money on some hardware. Basically there are two ways to do that: for one you can do it manually for every image or you can use a GPS receiver to record a GPX track while you take your pictures (you can either use a cheap GPS logger or a full fledged GPS receiver, maybe even your phone). So we somehow have to assign geo locations to the images. While the easiest way to get geotagged images is using a camera with a built-in GPS receiver (or an external receiver attached to the camera) most people don’t have that. So everyone using either the experimental builds from Pascal’s PPA, compiles darktable from git or has some other way to run the latest and greatest development version of darktable can try all of this stuff.Ī full fledged GPS receiver and a small logger Granted, a few details are still missing and I wouldn’t be surprised if a few quirks and bugs can be found, too, but nevertheless I decided that the code was ready for prime time and merged it back into master. Since it would be a pity to throw away all the great work Henrik did I kind of adopted the branch and set sails to add the missing bits and pieces to make geotagging a new feature of darktable. Things started to come together nicely and everything looked really promising, but unfortunately he was a little short in free time so the progress stalled and the code started to bitrot. Some day however Henrik decided to give it a try and started work in his geo branch. ![]() While that is a nifty feature for sure and really helpful when you take pictures outside of a studio we always had to say something along the lines of “sorry, we don’t have that yet”. For quite some time people have asked us for a way to geotag their images from within darktable. ![]()
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