ReadonlyaxisExpress ID of the IfcGridAxis.
ReadonlyendEnd endpoint [x, y, z] in renderer Y-up world space (metres).
ReadonlygridExpress ID of the owning IfcGrid.
ReadonlystartStart endpoint [x, y, z] in renderer Y-up world space (metres).
ReadonlytagAxis tag (e.g. "A", "1"); empty string when unauthored.
One grid axis: tag + endpoints in renderer Y-up world space (metres).