Offset stored in IFC file, how and where?

[Moult]

@Hans_Lammerts a note that I have found issues in those published documents. Apart from some naming mistakes, which may result in incorrect geolocation in IFC2X3, more importantly the documents do not seem to fully describe proper usage when it comes to referencing EPSG registry identifiers. The practical result of this is that geolocation may be stored in misleading and inconsistent ways - remember that the easting / northing / vertical elevation numbers are merely half the storey: identifying the CRSes and projections used are equally important. Please read this thread for a full description of the issues, which are still outstanding half a year later.

Geolocation standards in IFC2X3 and IFC4

I have been working with @john.mitchell, co-founder of buildingSMART Australia, and a domain expert in map conversions and CRS entities in IFC to establish standards on how to geolocate projects in both IFC2X3 and IFC4. We have had a couple of informal discussions in person, so I thought to bring the discussion online so that others could see and contribute. Proposal 1 The first issue is that IFC2X3 does not have geolocation entities. To mitigate this, we propose an official convention that al…

If you are working with Revit users, this document by OSArch describing how to achieve geolocation in Revit may be useful:

https://wiki.osarch.org/index.php?title=Revit_geolocation

Even more detailed reading here (though Revit is mentioned, it talks about the general principles too):

IFC Coordinate Reference Systems and Revit

Now that the theory is out of the way, here are some practical realities to expect when in the trenches, at least in Australia - but it may be similar where you are:

1. The elephant in the room: if it’s coming from Revit, it’s probably wrong, hence the need to document the workarounds so rigorously in the links above
2. I’ve noticed that most civil BIM IFCs stick to absolute coordinates for everything. They do not record the geolocation offset. This can cause issues if your IFC program is not capable of offsetting it at import time. Note that there are open source tools to fix this and offset IFC files, if needed.
3. Unless you train people explicitly, do not expect IFC2X3 projects to be properly geolocated. Very few implementers respect the EPsets for geolocation.
4. Even though geolocation may be read by some BIM programs, do not expect it to properly feed through things like solar analysis or weather files.
5. The geolocation data (easting, northings, elevation) and the “reference” data (lat, long, elevation) and the address data are not connected: expect mistakes and inconsistencies.