#### 8.7.2.2 IfcTransitionCode

The IfcTransitionCode indicated the continuity between consecutive segments of a curve or surface.

> EXAMPLE In ContSameGradient the tangent vectors of successive segments will have the same direction, but may have different magnitude.

Figure 118 illustrates transition types

> NOTE The figure is quoted from ISO 10303-42.

Figure 118 — Transition code

> NOTE Definition according to ISO/CD 10303-42:1992
> This type conveys the continuity properties of a composite curve or surface. The continuity referred to is geometric, not parametric continuity.

> NOTE Type adapted from transition_code defined in ISO 10303-42.

> HISTORY New Type in IFC1.0

Enumerated Item Definitions:

- discontinuous: The segments do not join. This is permitted only at the boundary of the curve or surface to indicate that it is not closed.
- continuous: The segments join but no condition on their tangents is implied.
- contsamegradient: The segments join and their tangent vectors or tangent planes are parallel and have the same direction at the joint: equality of derivatives is not required.
- contsamegradientsamecurvature: For a curve, the segments join, their tangent vectors are parallel and in the same direction and their curvatures are equal at the joint: equality of derivatives is not required. For a surface this implies that the principle curvatures are the same and the principle directions are coincident along the common boundary.

XSD Specification:

<xs:simpleType name="IfcTransitionCode">
<xs:restriction base="xs:string">
<xs:enumeration value="discontinuous"/>
<xs:enumeration value="continuous"/>
<xs:enumeration value="contsamegradient"/>
<xs:enumeration value="contsamegradientsamecurvature"/>
</xs:restriction>
</xs:simpleType>

EXPRESS Specification:

TYPE IfcTransitionCode = ENUMERATION OF (
| DISCONTINUOUS, CONTINUOUS, CONTSAMEGRADIENT, CONTSAMEGRADIENTSAMECURVATURE);
END_TYPE;

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