# 8.9.3.67 IfcSpiral

ABSTRACT This definition may not be instantiated

## 8.9.3.67.1 Semantic definition

Spirals are curves that revolve around a point while increasing its length. In general, these curves are parameterized in the following way: x = r(φ) cosφ y = r(φ) sinφ

In the case of the clothoid and higher order transition spirals, the parametrization is: x = ∫cos &Theta dl y = ∫sin &Theta dl

where &Theta is the deflection or bearing angle and dl the differential of the spiral length.

## 8.9.3.67.4 Formal representation

ENTITY IfcSpiral
ABSTRACT SUPERTYPE OF (ONEOF
(IfcClothoid
,IfcCosineSpiral
,IfcSecondOrderPolynomialSpiral
,IfcSeventhOrderPolynomialSpiral
,IfcSineSpiral
,IfcThirdOrderPolynomialSpiral))
SUBTYPE OF (IfcCurve);
Position : OPTIONAL IfcAxis2Placement;
END_ENTITY;