IFC 4.3.0.1 (IFC4X3) development

8.9.3.33 IfcEllipse

8.9.3.33.1 Semantic definition

An IfcEllipse is a curve consisting of a set of points whose distances to two fixed points add to the same constant.

The inherited SELF\IfcConic.Position.Location is the center of the IfcEllipse, and the inherited S_ELF\IfcConic.Position.Position.P[1] is the direction of the _SemiAxis1.

ellipse
Figure 8.9.3.33.A — Ellipse placement and parameterization

Definition of the IfcEllipse within the a three-dimensional position coordinate system is shown in Figure 8.9.3.33.A.

It is placed within the object coordinate system of an element of which it is a representation.

An ellipse is a conic section defined by the lengths of the semi-major and semi-minor diameters and the position (center or mid point of the line joining the foci) and orientation of the curve. Interpretation of the data shall be as follows:

C = position.location
x = position.p[1]
y = position.p[2]
z = position.p[3]
R1 = semi axis 1
R2 = semi axis 2

The ellipse is parameterized as:

$$ \lambda(u) = C + (R_1\cos(u))x + (R_2\sin(u))y $$

The parameterization range is 0 ≤ u <≤ 2π (0 ≤ u ≤ 360 degree). In the placement coordinate system defined above, the ellipse is the equation C = 0, where

$$ C(x,y,z) = \frac{x^2}{R_1^2} + \frac{y^2}{R_2^2} - 1 $$

The positive sense of the ellipse at any point is in the tangent direction, T, to the curve at the point, where

$$ T = (-C_y,C_x,0) $$

8.9.3.33.2 Entity inheritance

8.9.3.33.3 Attributes

# Attribute Type Description
IfcRepresentationItem (2)
LayerAssignment SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems

Assignment of the representation item to a single or multiple layer(s). The LayerAssignments can override a LayerAssignments of the IfcRepresentation it is used within the list of Items.

StyledByItem SET [0:1] OF IfcStyledItem FOR Item

Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve.

IfcCurve (1)
* Dim IfcDimensionCount

This attribute is formally derived.

IfcCurveDim(SELF)

The space dimensionality of this abstract class, defined differently for all subtypes, i.e. for IfcLine, IfcConic and IfcBoundedCurve.

IfcConic (1)
1 Position IfcAxis2Placement

The location and orientation of the conic. Further details of the interpretation of this attribute are given for the individual subtypes."

Click to show 4 hidden inherited attributes Click to hide 4 inherited attributes
IfcEllipse (2)
2 SemiAxis1 IfcPositiveLengthMeasure

The first radius of the ellipse which shall be positive. Placement.Axes[1] gives the direction of the SemiAxis1.

3 SemiAxis2 IfcPositiveLengthMeasure

The second radius of the ellipse which shall be positive.

Table 8.9.3.33.B

8.9.3.33.4 Formal representation

ENTITY IfcEllipse
 SUBTYPE OF (IfcConic);
	SemiAxis1 : IfcPositiveLengthMeasure;
	SemiAxis2 : IfcPositiveLengthMeasure;
END_ENTITY;

8.9.3.33.5 References

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