Robotics - ROS2 TF2

TF2 and Sim Time

When working with ROS2 and tf2, you may encounter the following warning when visualizing data in RViz or processing buffers:

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Warning: TF_OLD_DATA ignoring data from the past for frame base_link at time 4.294967 according to authority Authority undetectable

This message indicates that tf2 is dropping out-of-order or stale transforms because your TF publisher is using a “simulated time” (or older timestamps), while the receiver uses the default system clock. In that case, we can either hit the reset button, or we need to run nodes using use_sim_time

• You only need to drive the /clock topic when you’ve told your nodes / rviz to run in simulation time (i.e. you’ve set the use_sim_time parameter to true, by default, use_sim_time=false).
  • node->declare_parameter("use_sim_time", true);
  • or rviz use_sim_time:=true
• One example is replaying a bag and displaying on rviz. ros2 run rviz2 rviz2 --ros-args -p use_sim_time:=true

In your tf publisher node:

1. Enable Sim Time Parameter. In your node’s constructor or setup, set:

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node_->set_parameter(rclcpp::Parameter("use_sim_time", true));

1. Create a Clock Publisher. Declare and initialize a publisher for rosgraph_msgs::msg::Clock:

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rclcpp::Publisher<rosgraph_msgs::msg::Clock>::SharedPtr clock_pub_;
clock_pub_ = node_->create_publisher<rosgraph_msgs::msg::Clock>("/clock", 10);

1. Publish clock and tf together:

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// Build and publish clock
rosgraph_msgs::msg::Clock clk;
clk.clock = imu_msg->header.stamp;  // reuse the IMU’s timestamp
clock_pub_->publish(clk);
imu_tf_publisher_->publish(*imu_msg);

Transform Listener

Life Cycle

• tf2_ros::TransformListener starts its own subscription /tf, /tf_static:
  1. node_->create_subscription<tf2_msgs::msg::TFMessage>( … )
  2. stores that subscription in the same callback group / executor your node is using, and

Quirks

• rclcpp does not support callback in tf_listener.

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