IfcCrossProduct

函数定义

注：定义符合ISO/CD 10303-42:1992
此函数返回两个输入方向的向量（或交叉）积。输入方向必须是三维的。结果总是一个无单位的向量。如果输入方向是平行或反平行的，则返回一个零大小的向量。
注：功能改编自ISO 10303-42中定义的交叉产品。
IFC1.5中增加的新函数

EXPRESS Specification

FUNCTION IfcCrossProduct
  (Arg1, Arg2 : IfcDirection) 
    : IfcVector;
LOCAL
  Mag : REAL;
  Res : IfcDirection;
  V1,V2  : LIST[3:3] OF REAL;
  Result : IfcVector;
END_LOCAL;

  IF (NOT EXISTS (Arg1) OR (Arg1.Dim = 2)) OR (NOT EXISTS (Arg2) OR (Arg2.Dim = 2)) THEN
    RETURN(?);
  ELSE
    BEGIN
      V1  := IfcNormalise(Arg1)IfcDirection.DirectionRatios; 
      V2  := IfcNormalise(Arg2)IfcDirection.DirectionRatios;
      Res := IfcRepresentationItem() || IfcGeometricRepresentationItem () 
             || IfcDirection([(V1[2]*V2[3] - V1[3]*V2[2]), (V1[3]*V2[1] - V1[1]*V2[3]), (V1[1]*V2[2] - V1[2]*V2[1])]);
      Mag := 0.0;
      REPEAT i := 1 TO 3;
        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(Arg1, 0.0);
      END_IF;
      RETURN(Result);
    END;
  END_IF; 
END_FUNCTION;