Ian Keough

See [IfcSystem](http://www.buildingsmart-tech.org/ifc/IFC2x3/TC1/html/ifcproductextension/lexical/ifcsystem.htm) and [IfcPort](http://www.buildingsmart-tech.org/ifc/IFC2x3/TC1/html/ifcproductextension/lexical/ifcport.htm) for reference.

The serialization problem can probably be overcome with using a custom JsonConverter which, instead of trying to serialize all of Parent, just serializes the parent’s id. We do this something...

Extension methods won’t work on interfaces. Perhaps you could have a static class full of those utility methods. Like System.GetAllDownstream(IConnector connector).

Could you add me to your repo so I can pull it and try to build it and see what you’re seeing? Preferably whatever repo has the function code in...

There is already a [system type in IFC](http://www.buildingsmart-tech.org/ifc/IFC2x3/TC1/html/ifcproductextension/lexical/ifcsystem.htm). But it's basically just a group. If we do systems, I would like to make them traversable. We can still serialize to...

@wynged Apologies for the slow response here. Is the looping serialization problem due to having two way traversal? Would one way traversal work?

Thanks for the report @wynged. I'll take a look today.

Partially fixed in #773. Awaiting more doc updates.

I agree with the idea of the normal. This will likely be added when we support underlying surface equations for `Face`, like `Face.Surface.Normal`. Currently we only support planar surfaces so...

I think it would be nice to have convenience methods like `Vector3.IsHorizontal()` and `Vector3.IsVertical()`. Then you could do `Face.Surface.NormalAt(...).IsHorizontal`.