A planar joint is shown in the diagram below with the two bodies that it connects. A planar joint allows the two connected frames to translate along two axes and rotate about a third axis that is orthogonal to the two translational axes; this joint type prevents all of the other relative motions of the two frames. In the diagram below, the joint displacement vector, r, and joint angle, q, represent the relative translation and rotation respectively of the end frame, , with respect to the start frame, . In this example, the and frames are constrained by the joint to remain in the same plane.