The two crossing axes, e.g. a U axis and a V axis of the same grid.
OptionalOffsetsOffsets (metres): the distance of the point from the first and from the second axis, measured perpendicular to each (to its left, looking along the axis), and an optional height above the grid plane. Default [0, 0].
Two grid axes (IfcGridAxis ids) and optional offsets from them (metres).