Now that you have been introduced to the concepts of hierarchies and global/local/object transform space, we need to delve deeply into how rotations are handled in 3D. This is not an easy subject! 3D rotations are extremely complex mathematically and give even the most experienced 3D graphics engineer trouble when working with certain aspects of them.
There are two kinds of rotation calculations used in 3D graphics: Euler rotations, and quaternions. Euler rotations use three axes of rotation (x, y, and z) in a hierarchical manner (more on this later), while quaternion rotations use four axes of rotation (x, y, z, and w). Euler rotations are far more common in terms of accessibility to the user, and they are far more intuitive ...