#### 8.7.3.18 IfcSurface

| Surface
| Oberfläche

An IfcSurface is a 2-dimensional representation item positioned in 3-dimensional space. 2-dimensional means that each point at the surface can be defined by a 2-dimensional coordinate system, usually by u and v coordinates.

> NOTE Definition according to ISO/CD 10303-42:1992
> A surface can be envisioned as a set of connected points in 3-dimensional space which is always locally 2-dimensional, but need not be a manifold.

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

> HISTORY New entity in IFC1.5

Informal Propositions:

1. A surface has non zero area.
2. A surface is arcwise connected.

XSD Specification:

<xs:element name="IfcSurface" type="ifc:IfcSurface" abstract="true" substitutionGroup="ifc:IfcGeometricRepresentationItem" nillable="true"/>
<xs:complexType name="IfcSurface" abstract="true">
<xs:complexContent>
<xs:extension base="ifc:IfcGeometricRepresentationItem"/>
</xs:complexContent>
</xs:complexType>

EXPRESS Specification:

ENTITY IfcSurface

| ABSTRACT SUPERTYPE OF(ONEOF(IfcBoundedSurface, IfcSweptSurface))

| SUBTYPE OF (IfcGeometricRepresentationItem);

| DERIVE

Dim | : | IfcDimensionCount := 3;

END_ENTITY;

Attribute Definitions:

Dim | : | The space dimensionality of IfcSurface. It is always a three-dimensional geometric representation item. IFC4 CHANGE Derived attribute promoted from subtypes.

Inheritance Graph:

ENTITY IfcSurface

| ENTITY IfcRepresentationItem

| INVERSE

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

| ENTITY IfcGeometricRepresentationItem

| ENTITY IfcSurface

| DERIVE

Dim | : | IfcDimensionCount := 3;

END_ENTITY;

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