How to Read Telemetry Data Using MAVLink Protocol

To read telemetry data using MAVLink, you need to connect to the drone's communication port and parse incoming MAVLink messages. Use a MAVLink library to listen for messages like HEARTBEAT, GLOBAL_POSITION_INT, or ATTITUDE to get telemetry data such as position, orientation, and status.

Syntax

Reading telemetry data with MAVLink involves these steps:

• Connect to the drone's communication channel (serial, UDP, TCP).
• Receive raw MAVLink messages continuously.
• Parse messages to extract telemetry fields.
• Handle specific message types like HEARTBEAT or GLOBAL_POSITION_INT.

Example function calls and objects depend on the MAVLink library you use.

python

from pymavlink import mavutil

# Connect to the drone via UDP
master = mavutil.mavlink_connection('udp:127.0.0.1:14550')

# Wait for the first heartbeat message to confirm connection
master.wait_heartbeat()
print('Heartbeat from system (system %u component %u)' % (master.target_system, master.target_component))

# Read messages in a loop
while True:
    msg = master.recv_match(blocking=True)
    if not msg:
        continue
    print(msg)

Example

This example connects to a drone via UDP and prints its GPS position and attitude data from telemetry messages.

python

from pymavlink import mavutil

# Connect to the drone
master = mavutil.mavlink_connection('udp:127.0.0.1:14550')

# Wait for heartbeat
master.wait_heartbeat()
print(f'Connected to system {master.target_system}, component {master.target_component}')

while True:
    msg = master.recv_match(type=['GLOBAL_POSITION_INT', 'ATTITUDE'], blocking=True)
    if msg.get_type() == 'GLOBAL_POSITION_INT':
        lat = msg.lat / 1e7
        lon = msg.lon / 1e7
        alt = msg.alt / 1000.0
        print(f'GPS Position - Lat: {lat}, Lon: {lon}, Alt: {alt} m')
    elif msg.get_type() == 'ATTITUDE':
        roll = msg.roll
        pitch = msg.pitch
        yaw = msg.yaw
        print(f'Attitude - Roll: {roll:.2f}, Pitch: {pitch:.2f}, Yaw: {yaw:.2f}')

Output

Connected to system 1, component 1
GPS Position - Lat: 47.397742, Lon: 8.545594, Alt: 488.0 m
Attitude - Roll: 0.01, Pitch: -0.02, Yaw: 1.57
GPS Position - Lat: 47.397743, Lon: 8.545595, Alt: 488.1 m
Attitude - Roll: 0.02, Pitch: -0.01, Yaw: 1.58

Common Pitfalls

• Not waiting for a HEARTBEAT message before reading telemetry can cause connection issues.
• Using blocking reads without timeout may freeze your program if no messages arrive.
• Parsing wrong message types or ignoring message IDs leads to missing important telemetry.
• Forgetting to convert raw values (like latitude in 1e7 degrees) to human-readable units.

python

from pymavlink import mavutil

# Wrong: Not waiting for heartbeat
master = mavutil.mavlink_connection('udp:127.0.0.1:14550')
msg = master.recv_match(blocking=True)  # May block indefinitely or get unexpected message

# Right: Wait for heartbeat first
master.wait_heartbeat()
msg = master.recv_match(blocking=True)

Quick Reference

Key MAVLink messages for telemetry:

• HEARTBEAT: Confirms connection and system status.
• GLOBAL_POSITION_INT: GPS latitude, longitude, altitude.
• ATTITUDE: Drone orientation (roll, pitch, yaw).
• SYSTEM_TIME: Timestamp for synchronization.

Use recv_match(type=[...]) to filter messages by type.

Message	Description
HEARTBEAT	Connection and system status confirmation
GLOBAL_POSITION_INT	GPS coordinates and altitude
ATTITUDE	Drone orientation angles
SYSTEM_TIME	Timestamp synchronization

Key Takeaways

Always wait for a HEARTBEAT message to confirm MAVLink connection before reading telemetry.

Use a MAVLink library to parse messages like GLOBAL_POSITION_INT and ATTITUDE for telemetry data.

Convert raw telemetry values to human-readable units (e.g., latitude in degrees).

Filter messages by type to efficiently process only needed telemetry data.

Handle blocking calls carefully to avoid freezing your program.