IFC 4.3.x development

8.9.2.12 IfcTransitionCode

8.9.2.12.1 Semantic definitions at the entity

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 1 illustrates transition types

NOTE  The figure is quoted from ISO 10303-42.

"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

Items

DISCONTINUOUS
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.

8.9.2.12.1 Formal representations

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