(easting, northing, elevation) per vertex, in the file's length unit.
OptionalDescriptionOptionalFlagsIfcTriangulatedIrregularNetwork.Flags — mandatory and non-empty, unlike
most IFC list attributes. Defaults to a single 0 (no flag set).
OptionalGlobalSupply to make the GlobalId a function of the source id (§4.3).
1-based triples indexing Coordinates, per IfcTriangulatedFaceSet.
A single terrain surface: a TIN and the element that carries it.