Rotation orients a coordinate system about a rotation axis by a rotation angle measured in radians.
To help remember positive and negative rotation directions: open your hand, stick out your thumb,
aim your thumb in an axis positive direction, and curl your fingers around the axis.
The curl direction is a positive rotation.
These X3D scenes are adapted directly from the
original VRML 2.0 Sourcebook chapter examples.
Introduction to VRML97 SIGGRAPH98 course notes.