The navigation stack also needs to receive data from the robot odometry. The odometry is the distance of something relative to a point. In our case, it is the distance between base_link and a fixed point in the frame odom.
The type of message used by the navigation stack is nav_msgs/Odometry. We can see its structure using the following command:
$ rosmsg show nav_msgs/Odometry
The output of the preceding command is shown as follows:
std_msgs/Header header uint32 seq time stamp string frame_id string child_frame_id geometry_msgs/PoseWithCovariance pose geometry_msgs/Pose pose geometry_msgs/Point position float64 x float64 y float64 z geometry_msgs/Quaternion orientation float64 x float64 y float64 z float64 w float64[36] covariance geometry_msgs/TwistWithCovariance twist geometry_msgs/Twist twist geometry_msgs/Vector3 linear float64 x float64 y float64 z geometry_msgs/Vector3...