Product occurrences are placed in a right handed Cartesian coordinate system.
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4.8.1.1 Product Local Placement
Product occurrences can be placed in 3D space relative to where they are contained. Placement is defined by a relative position (X, Y, Z coordinates), a horizontal reference direction, and a vertical axis direction. At the outermost level, relative directions are defined according to representation context; for example, +X may point east, +Y may point north, and +Z may point up.
The IfcAxis2Placement3D diagram further confirms this.