IfcGetBasisSurface

Natural language names
Get Basis Surface
Semantic definitions at the function
Function Definition

NOTE  Definition according to ISO/CD 10303-42:1992
This function returns the basis surface for a curve as a a set of surfaces. For a curve which is not a curve on surface an empty set is returned.

NOTE  Function adapted from get_basis_surface defined in ISO 10303-42.

HISTORY  New function in IFC1.5

Formal representations
EXPRESS Specification

FUNCTION IfcGetBasisSurface
(C : IfcCurveOnSurface) : SET[0:2] OF IfcSurface;

  LOCAL
    Surfs : SET[0:2] OF IfcSurface;
    N : INTEGER;
  END_LOCAL;

  Surfs := [];
  IF 'IFCGEOMETRYRESOURCE.IfcPcurve' IN TYPEOF (C) THEN
    Surfs := [C\IfcPcurve.BasisSurface];
  ELSE
    IF 'IFCGEOMETRYRESOURCE.IfcSurfaceCurve' IN TYPEOF (C) THEN
      N := SIZEOF(C\IfcSurfaceCurve.AssociatedGeometry);
      REPEAT i := 1 TO N;
      Surfs := Surfs + IfcAssociatedSurface(C\IfcSurfaceCurve.AssociatedGeometry[i]);
      END_REPEAT;
    END_IF;
  END_IF;
  IF 'IFCGEOMETRYRESOURCE.IfcCompositeCurveOnSurface' IN TYPEOF (C) THEN

    (* For an IfcCompositeCurveOnSurface the BasisSurface is the intersection of the BasisSurface of all the segments. *)

    N := SIZEOF(C\IfcCompositeCurve.Segments);
    Surfs := IfcGetBasisSurface(C\IfcCompositeCurve.Segments[1].ParentCurve);
    IF N > 1 THEN
      REPEAT i := 2 TO N;
        Surfs := Surfs * IfcGetBasisSurface(C\IfcCompositeCurve.Segments[1].ParentCurve);
      END_REPEAT;
    END_IF;
  END_IF;
  RETURN(Surfs);

END_FUNCTION;

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