#### 8.6.3.6 IfcFaceBasedSurfaceModel

| Flächenmodell (basierend auf Einzelflächen)

The IfcFaceBasedSurfaceModel represents the a shape by connected face sets. The connected faces have a dimensionality 2 and are placed in a coordinate space of dimensionality 3.

> NOTE Definition according to ISO/CD 10303-42:1992
> A face based surface model is described by a set of connected face sets of dimensionality 2. The connected face sets shall not intersect except at edges and vertices, except that a face in one connected face set may overlap a face in another connected face set, provided the face boundaries are identical. There shall be at least one connected face set.
> A connected face set may exist independently of a surface model.

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

> HISTORY New entity in IFC2x.

Informal Propositions:

1. The connected face sets shall not overlap or intersect except at common faces, edges or vertices.
2. The fbsm faces have dimensionality 2.

XSD Specification:

<xs:element name="IfcFaceBasedSurfaceModel" type="ifc:IfcFaceBasedSurfaceModel" substitutionGroup="ifc:IfcGeometricRepresentationItem" nillable="true"/>
<xs:complexType name="IfcFaceBasedSurfaceModel">
<xs:complexContent>
<xs:extension base="ifc:IfcGeometricRepresentationItem">
<xs:sequence>
<xs:element name="FbsmFaces">
<xs:complexType>
<xs:sequence>
<xs:element ref="ifc:IfcConnectedFaceSet" maxOccurs="unbounded"/>
</xs:sequence>
<xs:attribute ref="ifc:itemType" fixed="ifc:IfcConnectedFaceSet"/>
<xs:attribute ref="ifc:cType" fixed="set"/>
<xs:attribute ref="ifc:arraySize" use="optional"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

EXPRESS Specification:

ENTITY IfcFaceBasedSurfaceModel

| SUBTYPE OF (IfcGeometricRepresentationItem);

FbsmFaces | : | SET [1:?] OF IfcConnectedFaceSet;

| DERIVE

Dim | : | IfcDimensionCount := 3;

END_ENTITY;

Attribute Definitions:

FbsmFaces | : | The set of connected face sets comprising the face based surface model.
Dim | : | The space dimensionality of this class, it is always 3.

Inheritance Graph:

ENTITY IfcFaceBasedSurfaceModel

| ENTITY IfcRepresentationItem

| INVERSE

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

| ENTITY IfcGeometricRepresentationItem

| ENTITY IfcFaceBasedSurfaceModel

FbsmFaces | : | SET [1:?] OF IfcConnectedFaceSet;

| DERIVE

Dim | : | IfcDimensionCount := 3;

END_ENTITY;

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