Correct usage of IfcMaterialLayerSetUsage for IfcSlab [modified 15-12-2006]
Based on IFC2x3
Initiator ISG Meeting-Berlin
Effects Extended Coordination View
Date 2006 02 24
For standard, prismatic slabs, the support of IfcMaterialLayerSetUsage is mandatory. This effects all usage of IfcSlab for floor slabs, roof slabs, base slabs, landings, etc.
The following conventions are agreed:
* Reference geometry: the extruded profile (plane) of IfcExtrudedAreaSolid.SweptSolid is the reference area. The IfcMaterialLayerSetUsage.OffsetFromReferenceLine is given as a distance from this plane.
* The reference coordinate system: coordinate system of the IfcExtrudedAreaSolid.Position.
* IfcMaterialLayerSetUsage.DirectionSense = Positve : the site of the plane where the positive extrusion direction is. TRUE means into the positive z-axis of the position as defined by the IfcExtrudedAreaSolid.Position. A positve value of IfcMaterialLayerSetUsage.OffsetFromReferenceLine would then point into the positive z-axis of the position.
* IfcMaterialLayerSetUsage.OffsetFromReferenceLine is the distance parallel to the base plane and perpendicular to the base (XY) plane. This is independent of a potential non-perpendicular extrusion given by IfcExtrudedAreaSolid.ExtrudedDirection <> 0.,0.,1.
* The Thickness of each IfcMaterialLayer shall be the parallel distance (measured perpendicular to the base plane). The TotalThickness of the IfcMaterialLayerSet is the sum of all layer thicknesses and in case of a perpendicular extrusion identical with IfcExtrudedAreaSolid.Depth
* IfcMaterialLayerSetUsage.LayerSetDirection = AXIS3 (always)
Figure 1: Applying a material layer set usage to IfcSlab being a horizontal slab.
Figure 2: Applying a material layer set usage to IfcSlab being a sloped roof slab.