AMCL中几处坐标转换

在看AMCL过程中，对坐标转移的关系不太清晰，整理下：

1、tf2::Transform map_pose = latest_tf_.inverse() * odom_pose_tf2;表示的是：

void AmclNode::savePoseToServer()
{
  // We need to apply the last transform to the latest odom pose to get
  // the latest map pose to store.  We'll take the covariance from
  // last_published_pose.
  tf2::Transform odom_pose_tf2;
  tf2::convert(latest_odom_pose_.pose, odom_pose_tf2);
  tf2::Transform map_pose = latest_tf_.inverse() * odom_pose_tf2;

  double yaw = tf2::getYaw(map_pose.getRotation());

  ROS_DEBUG("Saving pose to server. x: %.3f, y: %.3f", map_pose.getOrigin().x(), map_pose.getOrigin().y() );

  private_nh_.setParam("initial_pose_x", map_pose.getOrigin().x());
  private_nh_.setParam("initial_pose_y", map_pose.getOrigin().y());
  private_nh_.setParam("initial_pose_a", yaw);
  private_nh_.setParam("initial_cov_xx", 
                                  last_published_pose.pose.covariance[6*0+0]);
  private_nh_.setParam("initial_cov_yy", 
                                  last_published_pose.pose.covariance[6*1+1]);
  private_nh_.setParam("initial_cov_aa", 
                                  last_published_pose.pose.covariance[6*5+5]);
}

2、pose_new = pose_old * tx_odom_tf2;

void
AmclNode::handleInitialPoseMessage(const geometry_msgs::PoseWithCovarianceStamped& msg)
{
  boost::recursive_mutex::scoped_lock prl(configuration_mutex_);
  if(msg.header.frame_id == "")
  {
    // This should be removed at some point
    ROS_WARN("Received initial pose with empty frame_id.  You should always supply a frame_id.");
  }
  // We only accept initial pose estimates in the global frame, #5148.
  else if(stripSlash(msg.header.frame_id) != global_frame_id_)
  {
    ROS_WARN("Ignoring initial pose in frame "%s"; initial poses must be in the global frame, "%s"",
             stripSlash(msg.header.frame_id).c_str(),
             global_frame_id_.c_str());
    return;
  }

  // In case the client sent us a pose estimate in the past, integrate the
  // intervening odometric change.
  geometry_msgs::TransformStamped tx_odom;
  try
  {
    ros::Time now = ros::Time::now();
    // wait a little for the latest tf to become available
    tx_odom = tf_->lookupTransform(base_frame_id_, msg.header.stamp,
                                   base_frame_id_, ros::Time::now(),
                                   odom_frame_id_, ros::Duration(0.5));
  }
  catch(tf2::TransformException e)
  {
    // If we've never sent a transform, then this is normal, because the
    // global_frame_id_ frame doesn't exist.  We only care about in-time
    // transformation for on-the-move pose-setting, so ignoring this
    // startup condition doesn't really cost us anything.
    if(sent_first_transform_)
      ROS_WARN("Failed to transform initial pose in time (%s)", e.what());
    tf2::convert(tf2::Transform::getIdentity(), tx_odom.transform);
  }

  tf2::Transform tx_odom_tf2;
  tf2::convert(tx_odom.transform, tx_odom_tf2);
  tf2::Transform pose_old, pose_new;
  tf2::convert(msg.pose.pose, pose_old);
  pose_new = pose_old * tx_odom_tf2;

  // Transform into the global frame

  ROS_INFO("Setting pose (%.6f): %.3f %.3f %.3f",
           ros::Time::now().toSec(),
           pose_new.getOrigin().x(),
           pose_new.getOrigin().y(),
           tf2::getYaw(pose_new.getRotation()));
  // Re-initialize the filter
  pf_vector_t pf_init_pose_mean = pf_vector_zero();
  pf_init_pose_mean.v[0] = pose_new.getOrigin().x();
  pf_init_pose_mean.v[1] = pose_new.getOrigin().y();
  pf_init_pose_mean.v[2] = tf2::getYaw(pose_new.getRotation());
  pf_matrix_t pf_init_pose_cov = pf_matrix_zero();
  // Copy in the covariance, converting from 6-D to 3-D
  for(int i=0; i<2; i++)
  {
    for(int j=0; j<2; j++)
    {
      pf_init_pose_cov.m[i][j] = msg.pose.covariance[6*i+j];
    }
  }
  pf_init_pose_cov.m[2][2] = msg.pose.covariance[6*5+5];

  delete initial_pose_hyp_;
  initial_pose_hyp_ = new amcl_hyp_t();
  initial_pose_hyp_->pf_pose_mean = pf_init_pose_mean;
  initial_pose_hyp_->pf_pose_cov = pf_init_pose_cov;
  applyInitialPose();
}