Example of how to equery tf for a transform.

tf2_lookup_example.cc

  // In header:
  #include <tf2_ros/transform_listener.h>
  
  std::shared_ptr<tf2_ros::TransformListener> tf_listener_;
  tf2_ros::Buffer tf_buffer_;
  
  // In constructor:
  tf_listener_ = 
    std::make_shared<tf2_ros::TransformListener>(tf_buffer_);
  
  // ...
  
  // Get pose of camera.
  geometry_msgs::TransformStamped tf;
  try {
    // Need to remove leading "/" if it exists.
    std::string rgb_frame_id = rgb->header.frame_id;
    if (rgb_frame_id[0] == '/') {
      rgb_frame_id = rgb_frame_id.substr(1, rgb_frame_id.size()-1);
    }

    tf = tf_buffer_.lookupTransform(world_frame_id_, rgb_frame_id,
                                    ros::Time(rgb->header.stamp),
                                    ros::Duration(1.0/15));
  } catch (tf2::TransformException &ex) {
    ROS_ERROR("%s", ex.what());
    return;
  }