In some parts of the code, Euler angles are used (good interpretation), while in others, quaternions (easy calculation) are used.
For a better code quality, it would make sense to use a single representation throughout the whole code.
I think one good way to achieve this, would be to introduce something like a "rotation" class which uses quaternions internally but exposes (i.e. converts to) common (Euler Angles, Rotation Matrix, quaternion) representations.
In some parts of the code, Euler angles are used (good interpretation), while in others, quaternions (easy calculation) are used.
For a better code quality, it would make sense to use a single representation throughout the whole code.
I think one good way to achieve this, would be to introduce something like a "rotation" class which uses quaternions internally but exposes (i.e. converts to) common (Euler Angles, Rotation Matrix, quaternion) representations.