Tangent and curvature vector definition
 @TANGENT_CURVATURE_DEFINITION {
 @TANGENT_CURVATURE_NAME {TanCurName} {
 @CURVATURE_VECTOR { c_{1}, c_{2}, c_{3}}
 @TANGENT_VECTOR { t_{1}, t_{2}, t_{3}}
 @COMMENTS {CommentText}
 }
 }
Notes

The configuration of the beam is characterized by a curvature vector, c = {c_{1}, c_{2}, c_{3}} and a tangent vector, t = {t_{1}, t_{2}, t_{3}}, which is perpendicular to the beam's crosssection. Two parameters play an important role κ = c, and κ τ = t^{T} c, where κ is the curvature of the beam and τ its twist. Three types of beams can be defined

Straight beams: κ = 0 and τ = 0,

Circular beams: κ ≠ 0 and τ = 0, and

Helicoidal beams: κ ≠ 0 and τ ≠ 0,
where the latter two categories are also referred to as curved beams.

By default, the curvature and tangent vectors are initialized to a straightbeam configuration: the curvature vector vanishes, c = 0 and the tangent vector is t = {0, 0, 1}.

It is possible to attach comments to the definition of the object; these comments have no effect on its definition.