Offene Hüllle | |
Open Shell |
NOTE Definition according to ISO/CD 10303-42:1992
An open shell is a shell of the dimensionality 2. Its domain, if present, is a finite, connected, oriented, 2-manifold with boundary, but is not a closed surface. It can be thought of as a closed shell with one or more holes punched in it. The domain of an open shell satisfies 0 < Ξ < 1. An open shell is functionally more general than a face because its domain can have handles.
The shell is defined by a collection of faces, which may be oriented faces. The sense of each face, after taking account of the orientation, shall agree with the shell normal as defined below. The orientation can be supplied directly as a BOOLEAN attribute of an oriented face, or be defaulted to TRUE if the shell member is a face without the orientation attribute.
The following combinatorial restrictions on open shells and geometrical restrictions on their domains are designed, together with the informal propositions, to ensure that any domain associated with an open shell is an orientable manifold.
- Each face reference shall be unique.
- An open shell shall have at least one face.
- A given face may exist in more than one open shell.
The boundary of an open shell consists of the edges that are referenced only once by the face - bounds (loops) of its faces, together with all of their vertices. The domain of an open shell, if present, contains all edges and vertices of its faces.
NOTE Note that this is slightly different from the definition of a face domain, which includes none of its bounds. For example, a face domain may exclude an isolated point or line segment. An open shell domain may not. (See the algorithm for computing below.)
NOTE Entity adapted from open_shell defined in ISO 10303-42.
HISTORY New entity in IFC2x.
Informal Propositions:
# | Attribute | Type | Cardinality | Description | C |
---|---|---|---|---|---|
IfcRepresentationItem | |||||
LayerAssignment | IfcPresentationLayerAssignment @AssignedItems | S[0:1] | 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. | X | |
StyledByItem | IfcStyledItem @Item | S[0:1] | Reference to the IfcStyledItem that provides presentation information to the representation, e.g. a curve style, including colour and thickness to a geometric curve. | X | |
IfcTopologicalRepresentationItem | |||||
IfcConnectedFaceSet | |||||
1 | CfsFaces | IfcFace | S[1:?] | The set of faces arcwise connected along common edges or vertices. | X |
IfcOpenShell |
<xs:element name="IfcOpenShell" type="ifc:IfcOpenShell" substitutionGroup="ifc:IfcConnectedFaceSet" nillable="true"/>
<xs:complexType name="IfcOpenShell">
<xs:complexContent>
<xs:extension base="ifc:IfcConnectedFaceSet"/>
</xs:complexContent>
</xs:complexType>
ENTITY IfcOpenShell
SUBTYPE OF (IfcConnectedFaceSet);
END_ENTITY;