Robotics
Yaw
Definition
Yaw is the rotation angle about the z-axis in a specified roll-pitch-yaw convention. For a level robot in a z-up frame, it describes heading in the horizontal plane.
Also known as: Yaw angle
Updated
Turning in a declared frame
For an upright humanoid, a change in yaw can describe turning to face left or right. Roll and pitch describe the other two rotational components. ROS REP 103 defines its standard body axes as x forward, y left, and z up, and associates fixed-axis roll, pitch, and yaw with x, y, and z respectively.
The reference frame and rotation convention are part of the meaning. A yaw value without them is an incomplete orientation specification.
Positive yaw and compass bearings differ
Under ROS's right-handed convention, positive yaw turns counterclockwise when viewed from above a z-up frame. In a geographic east-north-up frame, zero yaw points east. REP 103 explicitly contrasts this with a compass bearing, which starts at north and increases clockwise.
A navigation system must convert between these conventions before comparing sensor readings or commanding a turn.
Heading is only one orientation component
Yaw alone does not describe a tilted robot's full orientation. Euler angles require a specified sequence, while a quaternion represents the complete rotation without angle-coordinate singularities. REP 103 recommends quaternions or rotation matrices ahead of angle representations for exchanging orientation data.
Sources
Related terms
Euler angles
Euler angles represent a three-dimensional orientation as an ordered sequence of three rotations about specified axes. Robotics often uses the term broadly to include roll-pitch-yaw conventions, so the exact rotation sequence must be specified.
Pose estimation
Pose estimation determines the position and orientation of an object or robot relative to a reference frame. For a rigid body in three-dimensional space, a full pose has three translational and three rotational degrees of freedom.
Inertial measurement unit
An inertial measurement unit is a sensor assembly that typically combines accelerometers and gyroscopes to measure specific force and angular velocity. Some devices also provide magnetometer readings or estimated orientation.