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Odometry
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Odometry is the use of data from motion sensors to estimate change in position over time. It is used in robotics  
by some legged or wheeled robots to **estimate their position relative to a starting location**.

.. tip::
   Origin of word "odometry": Greek hodos (way) + metron (measure).

Visual Odometry
===============
Visual odometry is the process of determining the position and orientation of a robot by analyzing the associated camera images.


VIO (Visual Inertial Odometry)
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Visual Inertial Odometry is like Visual Odometry but it also uses data from an Inertial Measurement Unit (IMU) to estimate the position 
and orientation of a robot.


ROS packages and messages
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* `geometry_msgs/Twist <https://docs.ros.org/en/noetic/api/geometry_msgs/html/msg/Twist.html>`_ - this expresses velocity in free space broken into its linear and angular parts

* `geometry_msgs/Pose <https://docs.ros.org/en/noetic/api/geometry_msgs/html/msg/Pose.html>`_ - a representation of pose in free space, composed of position and orientation

* `nav_msgs/Odometry <https://docs.ros.org/en/noetic/api/nav_msgs/html/msg/Odometry.html>`_ - this represents an estimate of a position (Pose) and velocity (Twist) in free space