IfcVectorDifference

Semantic definitions at the function

Function Definition

Definition from ISO/CD 10303-42:1992: This function returns the difference of the input arguments as (Arg1 - Arg2). The function returns as a vector the vector difference of the two input vectors. The input arguments shall both be of the same dimensionality but may be either directions or vectors. If both input arguments are vectors they must be expressed in the same units, if both are directions a unitless result is produced. A zero difference vector produces a vector of zero magnitude..

NOTE Corresponding STEP function: vector_different. Please refer to ISO/IS 10303-42:1994, p.109 for the final definition of the formal standard.

HISTORY New function in IFC Release 1.5

Formal representations

EXPRESS Specification

FUNCTION IfcVectorDifference
  (Arg1, Arg2 : IfcVectorOrDirection)
    : IfcVector;
LOCAL
  Result : IfcVector;
  Res, Vec1, Vec2 : IfcDirection;
  Mag, Mag1, Mag2 : REAL;
  Ndim : INTEGER;
END_LOCAL;

  IF ((NOT EXISTS (Arg1)) OR (NOT EXISTS (Arg2))) OR (Arg1.Dim <> Arg2.Dim) THEN
    RETURN (?) ;
  ELSE
    BEGIN
      IF 'IFCGEOMETRYRESOURCE.IFCVECTOR' IN TYPEOF(Arg1) THEN
        Mag1 := Arg1\IfcVector.Magnitude;
        Vec1 := Arg1\IfcVector.Orientation;
      ELSE
        Mag1 := 1.0;
        Vec1 := Arg1;
      END_IF;
      IF 'IFCGEOMETRYRESOURCE.IFCVECTOR' IN TYPEOF(Arg2) THEN
        Mag2 := Arg2\IfcVector.Magnitude;
        Vec2 := Arg2\IfcVector.Orientation;
      ELSE
        Mag2 := 1.0;
        Vec2 := Arg2;
      END_IF;
      Vec1 := IfcNormalise (Vec1);
      Vec2 := IfcNormalise (Vec2);
      Ndim := SIZEOF(Vec1.DirectionRatios);
      Mag  := 0.0;
      Res  := IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcDirection([0.0:Ndim]);

      REPEAT i := 1 TO Ndim;
        Res.DirectionRatios[i] := Mag1*Vec1.DirectionRatios[i] - Mag2*Vec2.DirectionRatios[i];
        Mag := Mag + (Res.DirectionRatios[i]*Res.DirectionRatios[i]);
      END_REPEAT;

      IF (Mag > 0.0 ) THEN
        Result := IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcVector( Res, SQRT(Mag));
      ELSE
        Result := IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcVector( Vec1, 0.0);
      END_IF;
    END;
  END_IF;
  RETURN (Result);
END_FUNCTION;