The IfcIndexedColourMap provides the assignment of colour information to individual faces. It is used for colouring faces of tessellated face sets. The IfcIndexedColourMap defines an index into an indexed list of colour information. The Colours are a two-dimensional list of colours provided by three RGB values. The ColourIndex attribute corresponds to the CoordIndex of the IfcTessellatedFaceSet defining the corresponding index list of faces. The Opacity attribute provides the alpha channel for all faces of the tessellated face set.
Figure 1 shows the use of IfcTriangulatedFaceSet with colours per face.
Figure 2 illustrates an IfcTriangulatedFaceSet represented by
Figure 2 — Indexed colour map geometry
HISTORY New entity in IFC4.
|1||MappedTo||IfcTessellatedFaceSet||Reference to the IfcTessellatedFaceSet to which it applies the colours and alpha channel.|
|2||Opacity||OPTIONAL IfcNormalisedRatioMeasure||The the opacity value, that applies equaly to all faces of the tessellated face set. 1.0 means opaque, and 0.0 completely transparent. If not provided, 1.0 is assumed (all colours are opque).|
> NOTE The definition of the alpha channel component for opacity follows the new definitions in image processing, where 0.0 means full transparency and 1.0 (or 2^bit depths^ -1) means fully opaque. This is contrary to the definition of transparency in IfcSurfaceStyleShading.
|3||Colours||IfcColourRgbList||Indexable list of lists of quadruples, representing RGB colours.|
|4||ColourIndex||LIST [1:?] OF IfcPositiveInteger||Index into the IfcColourRgbList for each face of the IfcTriangulatedFaceSet. The colour is applied uniformly to the indexed face.|
ENTITY IfcIndexedColourMap SUBTYPE OF (IfcPresentationItem); MappedTo : IfcTessellatedFaceSet; Opacity : OPTIONAL IfcNormalisedRatioMeasure; Colours : IfcColourRgbList; ColourIndex : LIST [1:?] OF IfcPositiveInteger; END_ENTITY;