Coordinate Frame

A defined origin and set of axis directions used to describe positions and orientations.

A coordinate frame — often just called a “frame” in robotics — consists of an origin and three mutually perpendicular axes; position is given as three numbers (x, y, z) and orientation as a rotation relative to those axes. The same physical point has different numeric coordinates in different frames, so any position, velocity, or force is meaningless without saying which frame it's expressed in. A single robot has many frames at once: a world frame fixed in the environment, a base frame fixed to the robot's base, and one for each link, camera, and gripper. In physics, “reference frame” also implies something about the observer's own motion, but in robotics engineering the two terms are mostly used interchangeably. ROS mandates right-handed coordinate frames throughout, and uses the TF tree to track the relationships between them.

ExampleA camera measures a cup at 0.6 meters directly in front of the lens, in the camera frame — but the arm needs the cup's position in the base frame, so the two must be related through a coordinate transformation.

Also called

Reference Frame, Frame

Related

World Frame · Base Frame · Camera Coordinate Frame · Coordinate Transformation · TF / tf2 Transform Tree · Pose

Sources

Wikipedia: Frame of reference
ROS REP 103: Standard Units of Measure and Coordinate Conventions