OptionalcolorPer-sub-mesh RGBA fill (0–1), present only when the source entity cut
into >1 distinct material — i.e. an IfcMaterialLayerSet wall/slab whose
layers each carry their IfcMaterial's surface-style colour, or a
frame+glass window. Renderers showing IFC materials use this so each
layer fills with its own colour instead of one colour for the whole
element; absent for single-material elements (keep the existing
per-ifcType / per-entity fill).
Source IFC entity expressId
IFC type name
True if from section cut, false if projection
OptionalisSet on the OPAQUE BASE polygon emitted for a multi-material entity: the
entity's full closed cross-section (built from the watertight union of all
its layer bands, so it always closes). It is drawn BEHIND the per-layer
colour fills in the 3D section overlay as a backstop, so a layer the
reconstruction cannot resolve still shows solid cut material instead of a
see-through hole. Carried only in Drawing2D.layerBaseCutPolygons (never in
cutPolygons), so the flat 2D drawing / export / measure paths never see it.
Model index for multi-model federation
2D polygon geometry
A polygon from section cut (used for hatching)