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#CV-2x3-145

clipping of round walls requires compatible geometry for wall body and restricted clipping planes
number
CV-2x3-145
based on
IFC2x3
effects
extended coordination view
date
26. Feb 2008
initiator
ISG meeting in Prague
summary clipping of round walls requires compatible geometry for wall body and restricted clipping planes

 

Description

Clippings of round walls based on restricted clipping planes, IfcPolygonalBoundedHalfSpace, had caused many tolerance issues.

Clipped round walls being exchanged as IfcWallStandardCase require an Axis representation with an IfcTrimmedCurve referring to a BasisCurve of type IfcCircle. The Body representation is an IfcBooleanClippingResult referring to an IfcExtrudedSolid and an IfcPolygonalBoundedHalfSpace (or IfcBoxedHalfSpace).

  1. Axis representation: RepresentationIdentifier : 'Axis'; RepresentationType : 'Curve2D'
  2. Body representation: RepresentationIdentifier : 'Body'; RepresentationType : 'Clipping'

There are two options:

  1. default: the Body representation is based on an foot print profile with true arc segments, IfcCompositeCurve with arc segments based on IfcTrimmedCurve referring to a BasisCurve of type IfcCircle. The clipping boundary of the IfcPolygonalBoundedHalfSpace, should then also be based on an IfcCompositeCurve with arc segments based on IfcTrimmedCurve referring to a BasisCurve of type IfcCircle. The geometry of both: the foot print of the wall and the clipping boundary could/should be identical for the overlapping part of the curve, or the clipping boundary is larger then the clipped body in all directions, but the critical clipping edge.
  2. fall back: the Body representation is based on an foot print profile with either true arc segments, or by a faceted polyline. The clipping boundary has to be larger then the clipped body in all directions, but the critical clipping edge.
NOTE: It is illegal to send a Body with a footprint being a faceted polyline AND a clipping boundary being another faceted polyline (both deemed to represent the same arc). It would lead in wrong clippings as the facetation might be different for the foot print and the clipping boundary.