BIM Befuddlement: LOD vs LOD


What the heck..?

How did we end up with the one acronym of LOD meaning two, maybe three quite different things ?

LOD isn’t a even particularly graceful or attractive term and sounds a bit too much like ‘CLOD‘ to me. Personally, traditional descriptions such as concept, schematic, detailed design & as-built were near enough.

Even worse, many people use the more common definition (Level of Development) but mean the other one (Level of Detail). To cap it off, the ‘D’ could be interpreted in the UK for ‘Level of Definition‘, which confusingly includes both Level of Detail and Level of Information….

This article explains the whole shemozzle in more detail.

Aussie BIM standards- we’ll just use someone else’s

Australia culturally sits somewhere between the UK (humour, sports, politics) and the US (lifestyle, business) so maybe that is why I often see project briefs that refer to both AIA G202 (US) and PAS 1192-2 (UK) and their differing definitions of LOD.

The Australian NATSPEC ‘National BIM Guide’ refers primarily to AIA E202 (although confusingly also refers elsewhere to UK documents). That just doesn’t make any sense and is akin to baseball pitch, bat and ball, but with some cricket rules thrown in.

I guess we could write our own BIM Standards, rather than ‘borrowing’ someone else’s and then complaining….  I am thinking of writing my own standard which will include something called LOD, which will stand for both ‘Level of Design’ and ‘Level of Documentation’.

Common misconception

A common misconception is that:

higher LOD = more geometry

Something that is geometrically detailed is not necessarily resolved or appropriate. For example, a very complex object might have been downloaded & dropped into a conceptual model. In isolation, the object might appear to be resolved, although it is not fit for purpose or does not meet the design intent.

Conversely, an item might be represented by a geometrically simple object, but contains all the information needed to fabricate or construct it in the form of attribute or ‘non-graphic information’  & therefore it meets the AIA/BIMForum definition of  higher LOD.

Unfortunately, the explanatory graphics in the BIM specifications suggest that geometry and LOD (either definition) always go hand in hand, and that it is necessary to model every  nut & bolt to construct something (which is not correct).

LOD graphic

Beyond LOD 500 (aka Stage 5)

Most building owners or asset managers don’t want every nut, bolt and other minutiae required for design and construction. In fact, this amount of information obscures the more important and valuable. Refer to my post BIM: Less is More

So, it shouldn’t be assumed that the the amount of model information always goes up over time. In fact, it could decrease substantially. Likewise, I am not interested in all the engineering that went into my car, but I just need a manual with information such as the tyre pressure & oil type.

The BIM information that is important for the ongoing operation of the asset might be geometrically simple, but data rich.

In the example of a commercial building this could include intangible information such as:

  • room, zone or lettable areas
  • clearance zones, for plant maintenance or servicing
  • spare parts list & maintenance requirements, or
  • a link to Operational & Maintenance Manuals.

The Solution ?

Short of renaming the LODs to something more sensible and creating yet more confusion, it seems too late to resolve this.

UK PAS 1192-2 does make more sense to me than the AIA standards (with the exception of the choice of LOD acronym) in particular the distinction between graphical detail and information.

The plain English use of ‘Concept’, ‘Build & Commission’, ‘Operation’ and so on, with the flexibility to determine necessary graphic detail and information level seems more logical & easier than the US approach.

Of course, this is not the first example of differing standards internationally (which side of the road to drive on, green vs red nautical markers etc).

But I do think it is unfortunate that there couldn’t be some agreement in this global era.