CV-2x3-129

Agreement on using the presentation layer assignment and layer with style 

Based on          IFC2x3

Initiator            ISG Meeting-Berlin

Effects              Extended Coordination View

Date                    2006 02 24

Description:

Since IFC2x3 the use of the property set Pset_Draughting (see CV-2x3-109) is deprecated and it shall no longer be used. The assignment to the presentation layer (i.e. the CAD layer) is handled by:

    * IfcPresentationLayerAssignment, or its subtype

    * IfcPresentationLayerWithStyle

Each shape representation of an IfcProduct can be assigned individually to an CAD Layer (PS: with the pre 2x3 Pset_Draughting, only the whole product could be assigned). In addition, each individual IfcRepresentationItem within a set of IfcRepresentation.Items can have its layer assignment. The following agreement is made:

    * first, check whether the IfcShapeRepresentation.LayerAssignments points to an IfcPresentationLayerAssignment (holding the CAD layer information),

    * second check, whether for an individual IfcGeometricRepresentationItem within the Items of the IfcShapeRepresentation an layer assignment override exists. If yes, assign it to the different layer

    * future, sensible restriction should be made on the potential overriding of the IfcShapeRepresentation.LayerAssignments by individual IfcGeometricRepresentationItem.LayerAssignment.

In addition, the implementer agreement is made, that each individual IfcShapeRepresentation or IfcGeometricRepresentationItem shall only have zero or one LayerAssignments.

Layer with style

In addition to the IfcPresentationLayerAssignment, the subtype IfcPresentationLayerWithStyle has to be supported for import and the style information has to be acknowledged.

The following entities are supported for IfcPresentationLayerWithStyle.LayerStyles

    * IfcCurveStyle

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