18 Sep LOD: Find Your Level
LOD. Three unassuming little letters that are currently causing big confusion for trade contractors and providers of Building Information Modelling, or BIM for short. So what is LOD? Brace yourselves dear readers, this takes some explaining…
Within the BIM universe, LOD stands for Level Of Development. However, another term regularly bandied around in BIM is Level Of Detail, creating acronym anxiety all round. To make matters worse the two terms are often mistaken for each other – not surprisingly – even though they describe different aspects of a model element. Lost yet? You’re not alone.
Thankfully NATSPEC, the National Building Specification not-for-profit, has undertaken the heroic task of compiling and maintaining a National BIM Guide for Australia. This is a suite of documents that has a red-hot go at defining the roles, procedures, approved software and documentation standards involved in implementing BIM on a project. Light bedtime reading it’s not, but it is a valuable resource for the Aussie construction industry, providing such useful nuggets as a Project BIM Brief Template to download.
Another useful NATSPEC document is a paper that focuses on the term LOD, explaining the concept of Level Of Development and acknowledging the confusion with Level Of Detail. In this paper NATSPEC recommends only ever using LOD as short-form for Level Of Development, which it describes like this: “LOD is a means of defining the extent to which model elements have been developed, from conception in the mind of the designer through to their construction and operation.” Alternatively, they say, “Use [the full term] Level Of Detail to describe graphic detail only.”
The way we interpret this at Drawable is that LOD primarily refers to the amount of data or information within an element in the model. If we’re talking an electrical Revit model, an element could be a distribution board, for example. At LOD 100, the only data that element would have is the description “distribution board”. LOD 200 could also state its preferred dimensions, LOD 300 might expand on its physical description, while LOD 400 would specify a particular board and comprise data such as its manufacturer and model number for ordering. LOD 500 comes at as built stage and would cover every bit of information deemed useful by the client, including purchase date, serial numbers etc for warranty and maintenance purposes.
Another important point NATSPEC makes is: “LOD should only be used to describe model elements” – i.e. your distribution board – “not models as a whole.” But customers talk about LOD as if it’s referring to the whole 3D model all the time, don’t they? Well, in that case, NATSPEC says to assume that “all individual model elements are at least of that LOD”.
“Graphic Detail” or “Level Of Detail”, on the other hand, we at Drawable interpret to mean what the representation of that distribution board actually looks like on the model. At its most basic this could just be a rectangle, whereas if we’re going to get totally fancy it could be a realistic illustration. The important thing to note here is that LOD and how pretty the element looks do not always coincide (although LOD 500 elements do tend to look schmick). However, unlike with LOD, there is no universally recognised grading system for Graphic/Level Of Detail.
At our parent company, Drawable, we have a fiendish plan to overcome all this confusion and have devised our own one-page Revit Specification Sheet, that enables us to glean close to all the information we need from our Revit/BIM customers. Following the KISS Principle, we avoid asking our trade customers to nominate LOD and instead use the more familiar terms of Shop Drawings, Revision Changes and As Builts. We will then work out the true LOD required when we get the full brief. Similarly, we’ve come up with our own ‘grades’ of graphic detail: Basic, Defined and Realistic. Of course one single-page form can’t cover all bases in the complex world of BIM, but we’re quietly confident it’s a sound start.
So if your contracting firm is new to BIM and LOD is making you think WTF, get in touch with a Drawable draftsman and we’ll give your Revit 3D models some TLC.