IFC 4.3.x development

8.10.3.9 IfcMaterialLayerWithOffsets

Change log

IFC4

added

8.10.3.9.1 Semantic definitions at the entity

IfcMaterialLayerWithOffsets is a specialization of IfcMaterialLayer enabling definition of offset values along edges (within the material layer set usage in parent layer set).

It defines the assignment of two offset values for a material layer in its intended use within a material layer set. Offsets are applied to the edges of layered elements (that is, in directions perpendicular to the layer set direction). Offsets shall not be used in layer set direction, that is, for modelling gaps (or overlaps) between layers; gaps shall be modeled as layers with appropriate material assignment for the void.

EXAMPLE  At the top of a standard wall, with shape representation 'SweptSolid', offset of a given layer can be specified in the direction of the extrusion (positive Z axis), applied at the start or end (extruded from bottom to top), and with a positive (extending above extrusion) or negative (ending below extrusion).

Take a standard wall with the outer material layer for the external isolation extending above extrusion by 100mm, but starting at the same base height. In this case the following values are set: > * OffsetDirection = .AXIS3. * OffsetValues[1] = 0.0 * OffsetValues[2] = 100.0 (default unit assumed to be mm)

NOTE  The 'Body' shape representation of an IfcWall or an IfcWallStandardCase may have multiple Items each being an IfcExtrudedAreaSolid corresponding to the IfcMaterialLayer and IfcMaterialLayerWithOffsets.

HISTORY  New entity in IFC4.

Informal Propositions:

  1. The OffsetDirection shall not be identical to the LayerSetDirection of the corresponding IfcMaterialLayerSetUsage.
  2. The attribute ReferenceExtent shall be asserted at the corresponding IfcMaterialLayerSetUsage.

Attribute use definition

The OffsetValues and OffsetDirection correspond to the definitions ReferenceExtent and LayerSetDirection at the IfcMaterialLayerSetUsage. Figure 1 shows an example of applying the OffsetValues to the material layers of a standard wall.

"IfcMaterialLayerWithOffsets_fig-1"

8.10.3.9.1 Attributes

# Attribute Type Description
IfcMaterialDefinition
AssociatedTo SET [0:?] OF IfcRelAssociatesMaterial FOR RelatingMaterial Use of the IfcMaterialDefinition subtypes within the material association of an element occurrence or element type. The association is established by the IfcRelAssociatesMaterial relationship.

> IFC4 CHANGE  The inverse attribute has been added.
HasExternalReferencesSET [0:?] OF IfcExternalReferenceRelationship FOR RelatedResourceObjectsReference to external references, e.g. library, classification, or document information, that are associated to the material.

> IFC4 CHANGE  The inverse attribute has been added.
HasProperties SET [0:?] OF IfcMaterialProperties FOR Material Material properties assigned to instances of subtypes of IfcMaterialDefinition.

> IFC4 CHANGE  The inverse attribute has been added.
IfcMaterialLayer
1 Material OPTIONAL IfcMaterial Optional reference to the material from which the layer is constructed. Note that if this value is not given, it does not denote a layer with no material (an air gap), it only means that the material is not specified at that point.
2 LayerThickness IfcNonNegativeLengthMeasure The thickness of the material layer. The meaning of "thickness" depends on its usage. In case of building elements elements utilizing IfcMaterialLayerSetUsage, the dimension is measured along the positive LayerSetDirection as specified in IfcMaterialLayerSetUsage.

> NOTE  The attribute value can be 0. for material thicknesses very close to zero, such as for a membrane. Material layers with thickess 0. may not be rendered in the geometric representation.

> IFC4 CHANGE  The attribute datatype has been changed to IfcNonNegativeLengthMeasure allowing for 0. as thickness.
3 IsVentilated OPTIONAL IfcLogical Indication of whether the material layer represents an air layer (or cavity).

* set to TRUE if the material layer is an air gap and provides air exchange from the layer to the outside air.

* set to UNKNOWN if the material layer is an air gap and does not provide air exchange (or when this information about air exchange of the air gap is not available).

* set to FALSE if the material layer is a solid material layer (the default).
4 Name OPTIONAL IfcLabel The name by which the material layer is known.
5 Description OPTIONAL IfcText Definition of the material layer in more descriptive terms than given by attributes Name or Category.
6 Category OPTIONAL IfcLabel Category of the material layer, e.g. the role it has in the layer set it belongs to (such as 'load bearing', 'thermal insulation' etc.). The list of keywords might be extended by model view definitions, however the following keywords shall apply in general:

* 'LoadBearing' — for all material layers having a load bearing function.

* 'Insulation' — for all material layers having an insolating function.

* 'Inner finish' — for the material layer being the inner finish.

* 'Outer finish' — for the material layer being the outer finish.
7 Priority OPTIONAL IfcInteger The relative priority of the layer, expressed as normalised integer range [0..100]. Controls how layers intersect in connections and corners of building elements: a layer from one element protrudes into (i.e. displaces) a layer from another element in a joint of these elements if the former element's layer has higher priority than the latter. The priority value for a material layer in an element has to be set and maintained by software applications in relation to the material layers in connected elements.

> NOTE  The layer priority at a connection may be overridden by the priority attributes of IfcRelConnectsPathElements if that relationship is used to establish a logical connection between two building elements having a layer structure.
ToMaterialLayerSet IfcMaterialLayerSet FOR MaterialLayers Reference to the IfcMaterialLayerSet in which the material layer is included.
IfcMaterialLayerWithOffsets
8 OffsetDirection IfcLayerSetDirectionEnum Orientation of the offset; shall be perpendicular to the parent layer set direction.
9 OffsetValues ARRAY [1:2] OF IfcLengthMeasure The numerical value of layer offset, in the direction of the axis assigned by the attribute OffsetDirection. The _OffsetValues[1]_ identifies the offset from the lower position along the axis direction (normally the start of the standard extrusion), the _OffsetValues[2]_ identifies the offset from the upper position along the axis direction (normally the end of the standard extrusion).

8.10.3.9.2 Entity inheritance

dot_inheritance IfcMaterialLayerWithOffsets IfcMaterialLayerWithOffsets IfcMaterialLayer IfcMaterialLayer IfcMaterialLayerWithOffsets->IfcMaterialLayer IfcMaterialDefinition IfcMaterialDefinition IfcMaterialLayer->IfcMaterialDefinition IfcMaterialDefinition_children 6 more... IfcMaterialDefinition_children->IfcMaterialDefinition

8.10.3.9.3 Formal representations

ENTITY IfcMaterialLayerWithOffsets
 SUBTYPE OF (IfcMaterialLayer);
	OffsetDirection : IfcLayerSetDirectionEnum;
	OffsetValues : ARRAY [1:2] OF IfcLengthMeasure;
END_ENTITY;