build a kinematic algorithm to measure 3d angles from frontal frame/video only

we need to analyse various angles of a golfer whilst they are mid action of a golf swing, it is very easy to get angles from x -y plane, however we need to calculate angles such as spine bend which require a good approximation of z coords, which has proven very hard to do , we need either a ratio based kinematic algorithm or another approach. currently we have been utilising a standard out of the box solution of mediapipe on python.