In order for RedEdge to properly geotag images, GPS data must be available to the camera. The easiest way to do this is to connect the GPS module provided with the camera* to the "GPS" port of the camera. A 6-pin to 6-pin cable is provided with your RedEdge for this purpose. Mount the GPS in a location that has a clear view of the sky.
For more advanced integrations, it is possible to do away with the dedicated GPS module by configuring your system to send GPS data to either the serial port or the ethernet port of the camera. Refer to the RedEdge Integration Guide for details on the pinout of the COMM connector of the camera.
For either serial or ethernet communication, see the API documentation. RedEdge supports MAVLINK for serial communications, a protocol that is commonly used in autopilots such as APM and Pixhawk. The MAVLINK messages that should be sent to the camera include GPS_RAW_INT and SYSTEM_TIME at a minimum. The ATTITUDE message is also helpful but not required.
*Note that the GPS module provided with your camera has been pre-configured. Brand new units of the same module may not function properly.