ROS2 Static Transform Broadcaster

🧠 Concept: TF2 — The Transform Tree

Every real robot has multiple coordinate frames: base_link (robot centre), camera_link (camera position), laser_link (LiDAR position). TF2 tracks where each frame is relative to others, forming a transform tree.

         world
           │
        base_link
        /        \
  camera_link   laser_link

When your navigation stack asks "where is the obstacle in base_link coordinates?", TF2 walks this tree to answer.

Static transforms are for frames that never move relative to each other (e.g. a fixed camera on the robot body):

from tf2_ros import StaticTransformBroadcaster
from geometry_msgs.msg import TransformStamped

broadcaster = StaticTransformBroadcaster(self)
t = TransformStamped()
t.header.frame_id = 'base_link'    # parent frame
t.child_frame_id  = 'camera_link'  # child frame
t.transform.translation.x = 0.2   # camera is 20cm in front
broadcaster.sendTransform(t)

Problem Statement

Broadcast a static coordinate transformation between two frames. This defines the physical relationship between robot parts (e.g., Lidar is 10cm above Base).

Requirements

• Create a node that broadcasts a static TF
• Parent Frame: world
• Child Frame: robot_base
• Translation: x=1.0, y=2.0, z=0.0
• Rotation: 0,0,0 (identity quaternion)

Input/Output Format

Output:

• Publishes to /tf_static topic.

⚠️ Common Pitfalls

• Publishing to /tf instead of /tf_static (static transforms should be latched and published once or rarely).
• Forgetting the timestamp (now()).

📚 Helpful Resources

• Writing a Static Broadcaster