I'm currently implementing a C++ solution to track motion of multiple objects. In that I have tracked points of those objects in a frame sequences such that multiple points in each frame. As a result of that I have x, y, z coordinates of those points of the entire frame sequence. By studying an already generated model I understood it consists of a joints system which move relative to each other. Every joint has a parent and their movements are written relative to its parent in Quaternion format. Therefore, I want to convert my x,y,z coordinates, which are in 3D space relative to same origin, to quaternion format which are written as relative to its parent. I can then use the quaternions to animate them.
I don't understand how to calculate the angle that it requires. Can you please provide me a sample code (in c++) or any useful resources to overcome this problem.