tf2.md

rclcpp: TF2

The TF2 library provides easy access to transformations. All of the examples below require a dependency on the tf2_ros package.

Broadcasting Transforms

#include <tf2_ros/transform_broadcaster.h>
std::unique_ptr<tf2_ros::TransformBroadcaster> broadcaster;

broadcaster = std::make_unique<tf2_ros::TransformBroadcaster>(nodePtr);

geometry_msgs::msg::TransformStamped transform;
transform.header.stamp = node->now();
transform.header.frame_id = "odom";
transform.child_frame_id = "base_link";

// Fill in transform.transform.translation
// Fill in transform.transform.rotation

broadcaster->sendTransform(transform);

Listening for Transforms

#include "tf2_ros/transform_listener.h"

std::shared_ptr<tf2_ros::Buffer> tf_buffer;
std::shared_ptr<tf2_ros::TransformListener> tf_listener;

rclcpp::Node node("name_of_node");

tf_buffer.reset(new tf2_ros::Buffer(node.get_clock()));
tf_listener.reset(new tf2_ros::TransformListener(*tf_buffer_));

Applying Transforms

TF2 can be extended by packages that provide implementations of transform. The _tf2_geometry_msgs package provides these for geometry_msgs. The example below uses geometry_msgs::msg::PointStamped - but this should work for any data type in geometry_msgs:

#include <tf2_geometry_msgs/tf2_geometry_msgs.h>

geometry_msg::msgs::PointStamped in, out;
in.header.frame_id = "source_frame";

try
{
  tf_buffer->transform(in, out, "target_frame");
}
catch (const tf2::TransformException& ex)
{
  RCLCPP_ERROR(rclcpp::get_logger("logger_name"), "Could not transform point.");
}

The transform function can also take a timeout. It will then wait for the transform to be available up to that amount of time:

tf_buffer->transform(in, out, "target_frame", tf2::durationFromSec(1.0));

Get Latest Transform

A common work flow is to get the "latest" transform. In ROS2, this can be accomplished using tf2::TimePointZero, but requires using lookupTransform and then calling doTransform (which is basically what transform does internally):

geometry_msgs::msg::PointStamped in, out;

geometry_msgs::msg::TransformStamped transform =
   tf_buffer->lookupTransform("target_frame",
                              in.header.frame_id,
                              tf2::TimePointZero);

tf2::doTransform(in, out, transform);