### How to calculate the angle between camera and a person?

I would like to calculate the human body angle with respect to the camera.
I have attached a screenshot for your kind reference.
If the person is looking into the camera then the angle is zero.

If the person is looking up then the angle is more than 0.
I have the pose coordinates of the person. I would appreciate your thoughts on this.
Thank you.

**EDIT: Duplicate Question**