Reference Information

Additional Information for Normative Rules

ALB021

This normative rule validates the three implementer agreements captured in three concept templates:

Case 1 - Horizontal Alignment Only

Only 1 IfcShapeRepresentation
- IfcShapeRepresentation
  - Item: IfcCompositeCurve
  - RepresentationIdentifier = Axis
  - RepresentationType = Curve2D

Case 2 - Horizontal and Vertical Alignment

2 IfcShapeRepresentations
- First IfcShapeRepresentation
  - Item: IfcCompositeCurve
  - RepresentationIdentifier = FootPrint
  - RepresentationType = Curve2D
- Second IfcShapeRepresentation
  - Item: IfcGradientCurve (using IfcCompositeCurve as BaseCurve)
  - RepresentationIdentifier = Axis
  - RepresentationType = Curve3D

Case 3 - Horizontal, Vertical, and Cant Alignment

2 IfcShapeRepresentations
- First IfcShapeRepresentation
  - Item: IfcCompositeCurve
  - RepresentationIdentifier = FootPrint
  - RepresentationType = Curve2D
- Second IfcShapeRepresentation
  - Item: IfcSegmentedReferenceCurve (using IfcGradientCurve as BaseCurve)
  - RepresentationIdentifier = Axis
  - RepresentationType = Curve3D

ALS016

This industry best practice rule performs geometric calculations to assess geometric continuity between successive IfcCurveSegment entities that make up an alignment representation.

This rule checks the shape representation (geometry) only and does not utilize any information in the semantic (business logic) definition of the alignment.

The Transition attribute on IfcCurveSegment is utilized to determine the model author’s intended continuity between segments.

A value of .CONTINUOUS. would mean that a warning for ALS016 could be raised positional discontinuity only (not tangency). Similarly, a value of .DISCONTINUOUS. would mean that a warning for ALS016 could not be raised, full stop.