Odom service interface

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Get Odometer Data

Introduction

the odometer service interface is used to subscribe to the position, direction, linear velocity, angular velocity and other leg_odom topic information of the robot. This topic uses nav_msgs::msg::Odometry message type containing information about the odometer issued by the robot chassis.

Topic Name	Topic type	role
leg_odom	nav_msgs::msg::Odometry	subscriber

Message Structure

std_msgs/Header header
string child_frame_id
geometry_msgs/PoseWithCovariance pose
geometry_msgs/TwistWithCovariance twist

Main Field Description

header: A standard ROS message header that contains a timestamp and coordinate system.

• stamp : Timestamp, indicating the time of data collection.
• frame_id : Coordinate system ID, indicating the coordinate system referenced by the odometer pose data.
• child_frame_id: Indicates the robot coordinate system referenced by the odometer twist data.

pose : The pose information of the robot, usually including the position ( position ) and direction ( orientation ).

• pose.pose.position : Position information stored through a three-dimensional array. The three elements of the array respectively represent the x, y, and z coordinate values of the geometric center of the fuselage under the World coordinate system (m)
• pose.pose.orientation : The direction quaternion information stored through the four-dimensional array is used to describe the rotation state

twist : The linear velocity and angular velocity information of the robot, used to represent the motion state of the robot.

• twist.twist.linear : Robot linear velocity, including x, y, and z components.
• twist.twist.angular : Robot angular velocity, which represents the rotational angular velocity of the fuselage around the z axis of the robot coordinate system (rad/s)

Callback Function Instance

void odometryCallback(nav_msgs::msg::Odometry::SharedPtr odom_data) {
  const auto& position = odom_data->pose.pose.position;
  if (isOdomInvalid(Eigen::Vector3d{position.x, position.y, position.z})) {
    SPDLOG_WARN("odometry data is invalid !!!");
    return;
  }
  geometry_msgs::msg::TransformStamped transform;
  // get current_pose_
  transform.transform.rotation = odom_data->pose.pose.orientation;
  transform.transform.translation.x = position.x;
  transform.transform.translation.y = position.y;
  transform.transform.translation.z = position.z;
  transform.header = odom_data->header;
  transform.child_frame_id = odom_data->child_frame_id;
  tf_broadcaster_->sendTransform(transform);
  // get current_vel_
  current_vel_[0] = odom_data->twist.twist.linear.x;
  current_vel_[1] = odom_data->twist.twist.linear.y;
  current_vel_[2] = odom_data->twist.twist.linear.z;
  current_vel_[3] = odom_data->twist.twist.angular.x;
  current_vel_[4] = odom_data->twist.twist.angular.y;
  current_vel_[5] = odom_data->twist.twist.angular.z;
}

Test Method

• subscribe to odometer messages:

ros2 topic echo /leg_odom

Precautions

• when obtaining odometer data, first ensure that the odometer ROS2 node has been started and is being released leg_odom topic.