IfcGetBasisSurface

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);

    IF ('IFCGEOMETRYRESOURCE.IfcCurveSegment' IN TYPEOF(C\IfcCompositeCurve.Segments[1])) THEN
      Surfs := IfcGetBasisSurface(C\IfcCompositeCurve.Segments[1]\IfcCurveSegment.ParentCurve);
    END_IF;
    IF ('IFCGEOMETRYRESOURCE.IfcCompositeCurveSegment' IN TYPEOF(C\IfcCompositeCurve.Segments[1])) THEN
      Surfs := IfcGetBasisSurface(C\IfcCompositeCurve.Segments[1]\IfcCompositeCurveSegment.ParentCurve);
    END_IF;

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




END_FUNCTION;