The navigation stack requires odometry data from the robot. The odometry is the displacement vector relative to a fixed inertial frame or world frame. Here, it is the displacement vector between the base_link and a fixed point in the odom frame. The message type used by the navigation stack is nav_msgs/Odometry. The following command shows its detailed structure which is shown in the following screenshot:
$ rosmsg show nav_msgs/Odometry
Odometry message structure
In the preceding screenshot, we can see that the pose has two structures that represent the position in Euler coordinates and the orientation of the robot using a quaternion. ...
