• For all entities, except shells, the principal material directions are aligned with the WCS axes.

• For shells, the principal material directions are defined by the parameterization of the surface, and that:

◦ Material direction 1 is parallel to the first parametric curve of the surface.

◦ Material direction 2 is set perpendicular to directions 1 and 3.

◦ Material direction 3 is perpendicular to the surface and aligned with the surface normal. For information about surface normals, see Surface Normals.