[IFC Rail] Spatial containment of IfcSpatialZone

[MatthieuPERIN]

How do we place IfcSpatialZone within the Spatial structure.

Two solutions are in my opinion feasible:

• Using IfcRelContainedInSpatialStructure with the idea that IfcSpatialZone are like IfcProduct that need to be contained within the spatial structure. Problem is that it somehow change the meaning of the relation (no schema change needed, it si teh solution as documented in SpatialDecomposition)
• Using IfcRelReferencedInSpatialStructure with the idea that IfcSpatialZone are not properly contained in a spatial structure. Problem is that the same relation will be used to link the IfcSpatialZone to the upper (the spatilastructure) and the lower (the Element attached to the SpatialZone), still no schema change needed...

Example provided from [IFC Rail] Urban Railway Story Line cabling below:

Ping @TLiebich, @SergejMuhic and @larswik !

[billeast]

Please clarify why IfcSystem is not being used to group IfcElements? IfcZone is for grouping IfcSpace only, is it not?

[MatthieuPERIN]

IfcSystem is meant to hold functional grouping only if I remember correctly.

The idea of using IfcSpatialZone is to have a spatial representation for the footprints (i.e. the RESERVATION predefined type) that can also be used to group object that share a common space. This object is no longer reserved to group IfsSpace in IFC 4.3, see Spatial Decomposition Documentation for more details.

[SergejMuhic]

IfcSpatialZone is supposed to be part of the spatial structure, so you can use IfcRelAggregates. See e.g. the Spatial Composition template documentation.

Before we start criticizing 😄 , let's just acknowledge that is has not been used a lot yet and therefore I would give it this pass.

Regarding alignment, there is no doubt that it shall be Spatial Containment.

We could consider a Spatial Decomposition of IfcFacilityPart into IfcFacilityPart where the below one has the footprint. I am really torn on this. Maybe you can come up with a solid proposal @MatthieuPERIN?

[MatthieuPERIN]

@SergejMuhic I was thinking that IfcRelAggregates was for decomposition (whole/part) but as IfcSpatialZone are not a formal  spatial decomposition I used IfcRelContainedInSpatialStructure to place them inside the spatial structure, and reserve IfcRelAggregate for decomposition of IfcSpatialZone into smaller IfcSpatialZone or IfcSpace.

Do you agree with that idea ?

In this example, a IfcFacilityPart for the multi tube might be a bit too much fine decomposition (not addressing the possible overlapping when the substructure passes under railway/roads....), this is why a IfcSpatialZone is better in my opinion: we need a RESERVATION of space to be able to place the tubes/ducts in the final infrastructure. Thus the addition of a geometry to IfcSpatialZone here is adequate in my opinion as the objectif is to have a spatial reservation = footprint geometry.

Thank for advice about Spatial Containement (IfcRelContainedInSpatialStructure) :bow:

[SergejMuhic]

Well the template does say that IfcSpatialZone should be part of the spatial structure, so with the current documentation I would see IfcSpatialZone to be related through IfcRelAggregates.