I have placed a Kinect(v2) at sagittal plane of a subject walking on a treadmill. Kinect(v2) provides 3D positional data (i.e x,y, and z column) (skeletal data) for all 25 number of joints. We know that not all joints of our body have 3 degrees of freedom (dof). But Kinect is giving 3D positional data for knee joint also which actually have 1 dof only.

My question is: do x,y, and z data of Kinect (placed at sagittal plane of a subject) represent the frontal, transverse, and sagittal plane data of a human body respectively? If it is not, then how to convert Kinect coordinate system data to body coordinate system data?