To enable complex movements, it's beneficial to be able to describe the robot state using a world reference frame, instead of using raw joint angles.
The robot's body pose in the world reference frame is represented as
Where
-
$x_b, y_b, z_b$ are cartesian coordinates of the robot's body center. -
$\phi, \theta,\psi$ are the roll, pitch and yaw angles, describing the body orientation.
The feet positions in the world reference frame are:
where
Solving the inverse kinematics yields target angles for the actuators.