Units for `IfcLengthMeasure` when using `IfcRigidOperation`

# Scenario

I'm using a combination of `IfcProjectedCRS` with `IfcRigidOperation` (there are no official examples in the specification to point to) as foreseen by:

https://github.com/buildingSMART/IFC4.3.x-development/blob/738df03670cd6208132d8fdcca902274afbdc6a8/docs/schemas/resource/IfcRepresentationResource/Entities/IfcRigidOperation.md?plain=1#L6

My CRS is defined in metres (EPSG:4647), while the project itself uses millimetres for length units - based on [this example](https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/annex_e/placements-and-gis-referencing/geographic-referencing-gk.html).

Also, I am using an offset following

https://github.com/buildingSMART/IFC4.3.x-development/blob/738df03670cd6208132d8fdcca902274afbdc6a8/docs/schemas/resource/IfcRepresentationResource/Entities/IfcRigidOperation.md?plain=1#L3

> using lengths to translate along x,y,z

# Problem

The example referenced above works, since `IfcMapConversion` provides the means to scale the `IfcLengthMeasure`s between the metres of the CRS and the defined default millimetres. The same attribute is not available in `IfcRigidOperation`.

# Question

Does this mean, that the `IfcLengthMeasure`s have to be provided in millimetres in my case? Or to generalize the question: in which unit are `IfcRigidOperation.FirstCoordinate`, `.SecondCoordinate` and `.Height` provided?

It seems that only the default unit as defined by the `IfcProject.UnitsInContext` could be assignable. This, however, seems a lot more restrictive than the possibility for a scaling factor between units as allowed for by `IfcMapConversion`. And also somewhat non-symmetrical, given `IfcMapConversion.Scale`.

# Clarification

Very much needed. I am open to the embodiment form. Perhaps a sentence or two in the specification? Another example?

Meta: I am unaware of the correct procedure or forum, how to internationally address this and come to a conclusion.

# Related

More or less related: #533 #710 #936