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;