这里记录一下cartographer里面的路标点是如何转换的，首先你要知道路标点在相机坐标系的位置（很多二维码读码器的关系恰好相反，是相机在二维码的坐标系），然后要知道相机坐标系和小车坐标系（一般为base_link）之间的关系。中间用tf_broadcaster_发出来便于查看是否设置正确

void Node::HandleLandmarkMessage(
    const int trajectory_id, const std::string& sensor_id,
    const cartographer_ros_msgs::LandmarkList::ConstPtr& msg) {
    
    
  absl::MutexLock lock(&mutex_);
  if (!sensor_samplers_.at(trajectory_id).landmark_sampler.Pulse()) {
    
    
    return;
  }

   map_builder_bridge_.sensor_bridge(trajectory_id)
          ->HandleLandmarkMessage(sensor_id, msg);

  geometry_msgs::TransformStamped stamped_transform;

  stamped_transform.header.stamp = ros::Time::now();
  stamped_transform.header.frame_id = "base_link";
        stamped_transform.child_frame_id = "QR_Code";
        stamped_transform.transform =  ToGeometryMsgTransform(ToRigid3d(msg->landmarks[0].tracking_from_landmark_transform).inverse());

        tf_broadcaster_.sendTransform(stamped_transform);