#### 8.6.3.18 IfcSweptDiskSolid

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An IfcSweptDiskSolid represents the 3D shape by a sweeping representation scheme allowing a two dimensional circularly bounded plane to sweep along a three dimensional Directrix through space.

The StartParam and EndParam parameter are optional, if not provided they default to the start and end of the Directrix. Only if the Directrix is given by a bounded or by a closed curve, it is permissible to omit the values of StartParam and EndParam.

If the transitions between consecutive segments of the Directrix are not tangent continuous, the resulting solid is created by a miter at half angle between the two segments. Informal proposition restricts the permissible angle between two non-tangent continuous segments.

Figure 115 illustrates an example.

- Directrix given as IfcCompositeCurve being tangent continuous between its segments
- Directrix being a bounded and open curve
- No StartParam and EndParam are provided, start and end default to start and end of the bounded curve of the Directrix

> NOTE Although the example shows a Directrix as a composite curve on a planar reference surface, the definition of IfcSweptDiskSolid is not restricted to be based on planer curves. However view definitions or implementer agreements may provide restrictions.

Figure 115 — Swept disk solid geometry

> NOTE Definition according to ISO/CD 10303-42:1992
> A swept disk solid is the solid produced by sweeping a circular disk along a three dimensional curve. During the sweeping operation the normal to the plane of the circular disk is in the direction of the tangent to the directrix curve and the center of the disk lies on the directrix. The circular disk may, optionally, have a central hole, in this case the resulting solid has a through hole, or, an internal void when the directrix forms a close curve.

> NOTE Entity adapted from swept_disk_solid defined in ISO 10303-42.

> HISTORY New entity in IFC2x2.

> IFC4 CHANGE The attribute StartParam and EndParam have been made optional.

Informal Propositions:

1. If the Directrix curve definition is not tangent continuous, the transition between the segments has to be within an acceptable limit of tangent discontinuity. Very sharp edges may result in nearly impossible miter. Implementer agreements may define acceptable limits for tangent discontinuity.
2. The segments of the Directrix shall be long enough to apply the Radius. In case of an arc segment forming part of the Directrix, its radius shall be greater then the disk Radius
3. The Directrix shall not be based on an intersecting curve.

XSD Specification:

<xs:element name="IfcSweptDiskSolid" type="ifc:IfcSweptDiskSolid" substitutionGroup="ifc:IfcSolidModel" nillable="true"/>
<xs:complexType name="IfcSweptDiskSolid">
<xs:complexContent>
<xs:extension base="ifc:IfcSolidModel">
<xs:sequence>
<xs:element name="Directrix" type="ifc:IfcCurve" nillable="true"/>
</xs:sequence>
<xs:attribute name="Radius" type="ifc:IfcPositiveLengthMeasure" use="optional"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

EXPRESS Specification:

ENTITY IfcSweptDiskSolid

| SUBTYPE OF (IfcSolidModel);

Directrix | : | IfcCurve;
Radius | : | IfcPositiveLengthMeasure;
InnerRadius | : | OPTIONAL IfcStrippedOptional;
StartParam | : | OPTIONAL IfcStrippedOptional;
EndParam | : | OPTIONAL IfcStrippedOptional;

| WHERE

DirectrixDim | : | Directrix.Dim = 3;
InnerRadiusSize | : | (NOT EXISTS(InnerRadius)) OR (Radius > InnerRadius);
DirectrixBounded | : | (EXISTS(StartParam) AND EXISTS(EndParam)) OR (SIZEOF(['IFCGEOMETRYRESOURCE.IFCCONIC', 'IFCGEOMETRYRESOURCE.IFCBOUNDEDCURVE'] * TYPEOF(Directrix)) = 1);

END_ENTITY;

Attribute Definitions:

Directrix | : | The curve used to define the sweeping operation. The solid is generated by sweeping a circular disk along the Directrix.
Radius | : | The Radius of the circular disk to be swept along the directrix. Denotes the outer radius, if an InnerRadius is applied.
InnerRadius | : | This attribute is optional, if present it defines the radius of a circular hole in the centre of the disk.

Formal Propositions:

DirectrixDim | : | The Directrix shall be a curve in three dimensional space.
InnerRadiusSize | : | If InnerRadius exists then Radius denoting the outer radius shall be greater than InnerRadius.
DirectrixBounded | : | If the values for StartParam or EndParam are omited, then the Directrix has to be a bounded or closed curve. IFC4 CHANGE New WHERE rule.

Inheritance Graph:

ENTITY IfcSweptDiskSolid

| ENTITY IfcRepresentationItem

| INVERSE

LayerAssignment | : | SET [0:1] OF IfcPresentationLayerAssignment FOR AssignedItems;
StyledByItem | : | SET [0:1] OF IfcStyledItem FOR Item;

| ENTITY IfcGeometricRepresentationItem

| ENTITY IfcSolidModel

| DERIVE

Dim | : | IfcDimensionCount := 3;

| ENTITY IfcSweptDiskSolid

Directrix | : | IfcCurve;
Radius | : | IfcPositiveLengthMeasure;
InnerRadius | : | OPTIONAL IfcStrippedOptional;
StartParam | : | OPTIONAL IfcStrippedOptional;
EndParam | : | OPTIONAL IfcStrippedOptional;

END_ENTITY;

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