MAVLink Log Format

QGroundControl allows you to generate plain MAVLink packet logs that can be replayed (with QGroundControl) to watch a mission again for analysis.

The format is binary:

• Byte 1-8: Timestamp in microseconds since Unix epoch as unsigned 64 bit integer
• Byte 9-271: MAVLink packet (263 bytes maximum packet length, not all bytes have to be actual data, the packet might be shorter. Includes packet start sign)

Debugging

To check your data, open your written file in a hex editor. You should see after 8 bytes 0x55. The first 8 bytes should also convert to a valid timestamp, so something either close to zero or around the number 1294571828792000 (which is the current Unix epoch timestamp in microseconds).

C++ Sketch for logging MAVLink

The code fragment below shows how to implement logging using C++ streams from the C++ standard library.

//write into mavlink logfile
const int len = MAVLINK_MAX_PACKET_LEN+sizeof(uint64_t);
uint8_t buf[len];
uint64_t time = getSystemTimeUsecs();
memcpy(buf, (void*)&time, sizeof(uint64_t));
mavlink_msg_to_send_buffer(buf+sizeof(uint64_t), msg);
mavlinkFile << buf << flush;