IfcBaseAxis

IfcBaseAxis

函数定义

注：根据ISO/CD 10303-42:1992的定义

此函数返回归一化正交方向u[1]、u[2]，如果合适，还返回u[3]。在三维情况下，对于完整的输入数据，u[3]位于axis3的方向，u[1]位于axis1在垂直于u[3]的平面上的投影方向，u[2]与u[1]和u[3正交，与axis2具有相同的意义。在二维情况下，u[1]在轴1的方向上，u[2]垂直于轴1，从轴2取其意义。对于不完整的输入数据，将导出相应的默认值。

注：根据ISO 10303-42中定义的基准轴调整功能。

IFC2x中的新函数

EXPRESS Specification

FUNCTION IfcBaseAxis
  (Dim : INTEGER;
   Axis1, Axis2, Axis3 : IfcDirection)
    : LIST [2:3] OF IfcDirection;

LOCAL
  U : LIST [2:3] OF IfcDirection;
  Factor : REAL;
  D1, D2 : IfcDirection;
END_LOCAL;

  IF (Dim = 3) THEN
    D1 := NVL(IfcNormalise(Axis3), IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcDirection([0.0,0.0,1.0]));
    D2 := IfcFirstProjAxis(D1, Axis1);
    U  := [D2, IfcSecondProjAxis(D1, D2, Axis2), D1];
  ELSE
    IF EXISTS(Axis1) THEN
      D1 := IfcNormalise(Axis1);
      U  := [D1, IfcOrthogonalComplement(D1)];
      IF EXISTS(Axis2) THEN
        Factor := IfcDotProduct(Axis2, U[2]);
        IF (Factor < 0.0) THEN
          U[2].DirectionRatios[1] := -U[2].DirectionRatios[1];
          U[2].DirectionRatios[2] := -U[2].DirectionRatios[2];
        END_IF;
      END_IF;
    ELSE
      IF EXISTS(Axis2) THEN
        D1 := IfcNormalise(Axis2);
        U  := [IfcOrthogonalComplement(D1), D1];
        U[1].DirectionRatios[1] := -U[1].DirectionRatios[1];
        U[1].DirectionRatios[2] := -U[1].DirectionRatios[2];
        ELSE
          U := [IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcDirection([1.0, 0.0]),
                IfcRepresentationItem() || IfcGeometricRepresentationItem () || IfcDirection([0.0, 1.0])];
      END_IF;
    END_IF;
  END_IF;
  RETURN(U);
END_FUNCTION;

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