EXIF refers to exchangeable image file format, a standard for storing data in images.
This can be considered as metadata about the image, annotating the location, timestamp, type of device used to capture the image, and more. Typical cameras (including smartphones) save EXIF data automatically, but the specifics depend on the device—for instance, the device needs to have GPS in order to write geolocation information into the EXIF data upon capture. There are programs that enable to add information to EXIF post-capture (e.g. add geotags to images).
To upload an image to Mapillary, the minimal information required in the EXIF data is the GPS position and the capture time of the images.
- GPS position—both GPS GPSLongitude and GPS GPSLongitude are required.
- Capture time—one of the following fields is required: EXIF DateTimeOriginal, EXIF DateTimeDigitized, EXIF DateTime, or GPS GPSDate.
You can see some technical documentation about editing the EXIF field here.
Manipulating EXIF data for images captured with the Mapillary mobile apps
It might be useful to know that the Mapillary mobile apps normally only write EXIF information to the images during upload or during transfer from an external camera—not at the time of capture. (In iOS, there is also a special button for writing the EXIF information without uploading.) Also, the Mapillary mobile apps write GPS information into the ImageDescription field and the Mapillary system will prefer that to the GPSLongitude and GPSLatitude fields.
Therefore, if you export the images from your phone in a manner that adds EXIF data, and edit their location information by modifying the GPSLongitude and GPSLatitude fields, these edits will not be seen on the Mapillary database since it will still read the GPS data from the ImageDescription field.
To avoid writing any location information into the ImageDescription field, you need to copy the images you've captured via the mobile app straight from your phone or camera's memory, without transferring or adding EXIF data. That way you can edit the GPSLongitude and GPSLatitude fields (either manually or from a recorded GPX track) in a way that lets them be recognized by the Mapillary system.