- The GPX format
- Synchronizing GPS Logger and the camera.
- Using Final Selection to synchronize our images with GPX files
- GPS Logger GPL for Android and iOS
It was the year 2012 when together with my friend David we set off from Saint Jean Pied de Port to Santiago de Compostela. After 36 days including Santiago – Vigo on foot I had 4 full compact-flash up photos. My idea was to document the stages photographically, but on the fourth day, tired of writing down in a little notebook the range of images I had taken and where they belonged, I left the task. Of those days, in addition to getting clear one of the coolest experiences of my life, I also came with wanting to get a GPS to take me to the adventures …
This is where the interest begins with GPS tracking devices.
It is increasingly common to see cameras with a built-in GPS device. This device is very useful when we seek to document the photos well since it allows us to geolocate them automatically. The downside is that this device is not usual in medium-low range cameras, assuming a significant outlay if we want to enjoy the service. In addition we find that the GPS of these cameras uses the battery of the same to operate, reducing considerably its autonomy.
What alternatives do we have to a GPS integrated in the camera? Easy, a GPS stuffed in your pocket. Today there are many devices that can help us geolocate our photos. From almost any mobile phone with Android or iOS using the appropriate app to the entire range of Garmin watches, for example. These devices provide us with a lot of information about our route in real time, but the functionality that interests us for the subject that concerns us is their “GPS Logger“.
But how does it work? It is simple, the device triangulates our position using the network of available satellites and according to the precision that we have configured it saves that position and the date and time in which it took it in an XML file, called GPX.
When I speak of precision I refer to the time that elapses since the device keeps one position and the next. Depending on what we have planned to do, we must choose the one that suits us best. For example, if we choose a precision of 1 second when we finish our route we will have a GPX file of a considerable size, in exchange we will have an exact location of our photos. (except when the satellite connection fails)
This way if we think about doing a report on a vehicle, the more accurate the better because in 1 second you can travel many meters. On the other hand, if we go on foot we can allow us to establish an accuracy of 2, 3 or even 5 seconds.
Later we will use this GPX file to compare it with the date and time of our photos. In this way we will know where they were made and we can geolocate them. Here comes Final Selection action! he will be in charge of collating dates, hours, latitudes and longitudes and geolocalizing our beloved photos!
THE GPX FORMAT
A GPX file, or GPS eXchange Format (GPS Interchange Format) is an XML schema designed to transfer GPS data between applications. It is used to describe points, routes and routes. In our case, what really interests us about the information stored in the file are the coordinates of Latitude and Longitude in addition to the time in which they were stored.
SYNCHRONIZING GPS LOGGER AND THE CAMERA
Since we will use the GPX file to compare the position dates with the dates and times in which the photos were taken, we must correctly synchronize our “gps logger” and our camera. For this, we only have to establish exactly the same date and time in both devices.
USING FINAL SELECTION TO SYNCHRONIZE OUR IMAGES WITH GPX FILES
Simply drag the GPX file of the route to the program so that it recognizes it and launch the management form. We can also use the menu “File-> Import GPX file”
We must choose the folder where the images we want to locate are located and after analyzing them we will have information like the following …
Once the program analyzes the GPX file and compares it with the images, they are established in two different states.
EXACT, this status is set when an exact time match has been found between the date on which the photograph was taken and the saved GPS position. By default, the program will always try to find the exact position. Day, month, year, hour, minute and second.
APPROXIMATE, cwhen the program does not find the exact position of the photo, it uses the value set as an option in “GPX Time Correction”. It will search within a range of X seconds from the date of the photo. If we do not establish a precision of 1 second in our “gps logger” this will be the most usual. Normally with 5 seconds we should have enough precision.
MODIFIED, this state is manual. Since in theory everything works great, but in practice it is very different, we find many factors that can negatively influence when determining our position. The loss of satellite signal, for example. Therefore, if we need to fine-tune the location of a photo, we can do it manually by searching for its exact location on the map. “Clicking” on the point you want will establish the new latitude and longitude coordinates. At this moment the state of the photo will change to the one that concerns us.
Once we perform the previous analysis and verify that the photos are assigned their
GPS coordinates, we just have to save them inside the images.
GPS LOGGER GPL FOR ANDROID AND IOS
Although a specific device is recommended given its accuracy, stability and autonomy, we can use a mobile phone as “gps logger”
There are several applications that do this function, including this GPS Logger of Basic Air Data, whose source code is GPL and has no adds or bagpipes.
Fully recommended to save our routes from your mobile.