Label
Concept definition
Given a right-handed orthonormal 3D coordinate system bound to an <OBJECT>, where the first axis of the coordinate system is directed through the front of the <OBJECT> and the second axis is directed through the right side of the <OBJECT>, the roll angle is the rotation about the first axis, with the positive rotation angle specified using the right-hand rule.
Narrative
The figure shows a positive value roll angle (about the roll axis, which in this case is labeled as the x-axis).
http://standards.iso.org/ittf/PubliclyAvailableStandards/index.html